1. Frequency of average occurrences of mild, moderate, and severe drought events
The average frequency of different drought events (averaged over 165 stations), calculated based on Eq. 2 clearly depicts of the prevalence of mild drought across all three time periods, followed by the moderate and severe drought (Table 3). It is interesting to note that as the temporal scale expands; the average frequency of drought also increases, highlighting the increased impact of seasonal precipitation over longer durations in arid regions such as Rajasthan (Bhattacharyya and Sreekesh, 2022). The average increase in drought events is more pronounced at shorter time scale (i.e., from 3-month to 6-month) than relatively longer time scale (i.e., from 6-month to 12-month). This is because most of the precipitation in this region is seasonally concentrated between late June and September (Bhattacharyya and Sreekesh, 2022).
Table 3
Average occurrences of Mild, Moderate and Severe Drought for different time scale during 1988–2021
|
Drought
|
Range of SPI
|
for 3 Months SPI
|
Frequency for 6 Months SPI
|
Frequency for 12 Months SPI
|
|
Severe Drought
|
Above − 2
|
1.77
|
3.21
|
4.41
|
|
Moderate Drought
|
-1.5 to -2
|
4.13
|
6.30
|
6.61
|
|
Mild Drought
|
-0.99 to -1.5
|
9.55
|
14.60
|
14.09
|
<Insert Table 3 here>
The temporal variations of mild, moderate, and severe drought also depict the same pattern where mild events are more frequent at all time scales (SPI3, SPI6, SPI12) followed by moderate and severe events (Figure. 2). Notably, in 2002, the total number of severe drought events was significantly higher than the other two categories that are found in all time-scales. Based on the fluctuations in the frequency of occurrence of drought events, the study period can be divided into two phases i.e., before 2002 and after 2002. In the first phase (1988–2002), an increase in the occurrences of severe drought is observed. During the second phase (2003–2021), severe drought events declined (Figure. 2). The temporal pattern of the drought events reflects the decadal/multi-decadal variability of drought occurrences in the state (Figure. 2). The multi decadal variability of drought is linked to the variability in rainfall which is more common in south west monsoon dominated regions like Rajasthan (Ghosh et al. 2016).
<Insert Fig. 2 here>
2.2 Spatial patterns of different categories of drought events
The investigation focuses on examining the spatial distribution of drought occurrences within the framework of three distinct drought categories: mild, moderate, and severe, as delineated by the Mackee classification scheme (Table 2). The objective of the investigation is to comprehend the geographical areas that are susceptible to varying intensities of drought events across different temporal scales. The frequency of drought events within each category is determined by quantifying the occurrences where the SPI value surpasses the predefined threshold value during the 34 years of time span (1988–2021). This investigation reveals that the occurrences of diverse drought event categories exhibit spatial variations across the region of Rajasthan.
<Insert Fig. 3 here>
Based on the analysis, it can be deduced that the state experiences approximately one or two severe drought events across different temporal scales, indicating a low frequency of such occurrences (Fig. 3m-q). The severe drought events are observed exclusively during SPI3-June and SPI3-September; whereas SPI3-March and SPI3-December do not exhibit any severe drought conditions (Fig. 3m-q). During the time period of SPI3-September, the state face more severe drought-like conditions compared to SPI3-June. Throughout the SPI3-June period, all agro-climatic regions within the state encounter the same count of severe events (Fig. 3m). The pattern of severe event occurrences during the SPI3-September timeframe extends from the northern region of the state to the central part, encompassing the northern tip of the irrigated zone, the northwestern plains, and the transitional plain of inland drainage. The occurrence of severe drought events is less during the time scale SPI6-June compared to SPI6-December (Fig. 3o & p). Sub-humid zones of the South Eastern plains along with small pockets in the zone of the semi-arid eastern plain are the most prone region to severe drought events during the SPI6-June. While during SPI6-December time the occurrence of more severe drought events is seen in the northern and the central part of the state covering agro climatic zones of transitional plain of inland drainage along with southeastern part of the district Bikaner, transitional plain of inland drainage, part of transitional plain of Luni basin and semi-arid eastern plain. In order to mark the zones prone to different category of drought based on the annual rainfall, SPI12-December is used. SPI12-December indicates that north western and central part of the state faces more severe events compared to the other part of the state. The flood prone eastern plain, humid south eastern plain, humid southern plain along with districts Jalore and Udaipur faces the lowest risk of occurrence of severe drought. Looking at the occurrence of pattern of severe drought event during the different time scales, it can be inferred that it is the northwestern and central part of the state which is more prone to severe events.
The count of occurrence of number of moderate drought events is more compared to severe drought events. During the October – December months except the district Churu, Jhunjhunu and Hanumangarh the state does not faces any moderate drought like condition .During the SPI3-March time scale, the north eastern part of the agro climatic zone Internal drainage dry zone and eastern part of zone Irrigated north western plain covering districts Hanumangarh, Churu and Jhunjhunu is most prone to the moderate drought events. During SPI3-June majority of the state faces rainfall deficit condition except for the western most part of the state, and the zone which falls under the major risk (high probability occurrence) of moderate event are the Humid southern plains, Humid South Eastern Plain, north eastern region of zone transitional plain of Internal drainage zone and Irrigated north western plain. The zone which is under the low risk is the hyper arid partial irrigated zone. The risk of occurrence of moderate drought events is low and is equally distributed over the state during the SPI3-September. The spatial pattern of moderate drought events during SPI6-June time period indicates that all the zones of the state faces low risk of occurrence of moderate drought events. Exceptions are the districts Bikaner, Ganganagar, Jaislamer, Pali and Dungarpur of Irrigated north western plain and hyper arid partial irrigated zone which face comparative more risk. During the SPI6-December time period, the zone flood prone eastern plain along with districts Jaisalmer (hyper arid partial irrigated zone) and Jalore (hyper arid partial irrigated zone) faces high risk of occurrence of the moderate drought event. During this time period the central part of the state faces the lowest risk of the occurrence of the moderate drought events. Long term SPI12-December time period indicates that the districts Jaisalmer and border area of Jalore and Sirohi is most prone to the occurrence of moderate drought events while the central part of the state i.e. districts Bikaner, Nagaur, Pali, Jhalawar, Kota faces no risk of occurrence of moderate drought event.
The count of occurrence of mild events is more compared to the moderate and severe drought (Fig. 3a-f). SPI3-June faces the highest risk of occurrence of mild drought events compared to the other time scale. In SPI 3 time scale, the SPI3-December does not face any mild drought event along with the severe and moderate drought events. Looking at the pattern and count of occurrence of mild events for SPI3-March, the north eastern part of the state covering the Irrigated North Western plain ,Bikaner district from the Hyper arid partial irrigated zone, Churu, Jhunjhunu, Sikar district from Transitional plain of Internal drainage, and districts Alwar and Bharatpur from flood prone eastern plains is most prone to drought. During SPI3-June, the mild drought events is scattered majorly towards the zones located in the western part of the Aravalli range and dominantly occurring in the districts of Jaisalmer, Barmer, Jodhpur, Nagaur and Bikaner. The Sub humid south eastern plain, Humid south eastern plain eastern part of eastern semi-arid eastern plain has the low risk of occurrence of mild events .The SPI3-September faces the low risk compared to SPI3-June and the flood prone eastern plain, humid southern plain, humid south eastern plain along with districts Barmer and Jalore falls under high risk comparatively to the other part of the state. Time period SPI6-June shows that during first half of the year almost whole of the state is equally prone to mild drought events except sub humid south eastern plain along with districts Tonk and northern Dungarpur who is least prone to mild events comparatively. The second half of the year that is SPI6-December faces low risk of occurrence of mild events compared to first half of the year. The spatial pattern of mild events occurrence during SPI6-December indicated that districts Jaisalmer and Banswara are comparatively most prone to mild events. Except the above two mentioned districts the state is more or less equally prone to mild drought events. Long term SPI12-December indicates that northern and south eastern part of the state is majorly prone to mild drought occurrence compared to the other parts of the state covering Hyper arid partial irrigated zone, Irrigated North western plain, humid southern plain, semi-arid eastern plain flood prone eastern plain and zone humid south eastern plains etc.
The spatial distribution pattern of three distinct drought categories across different temporal scales reveals that mild drought occurrences are most prevalent, followed by moderate drought, while severe drought events exhibit the lowest frequency within the designated time period of 1988–2021. The spatial pattern further indicates that severe drought primarily occurs during the months of July, August, and September, whereas a moderate and mild drought event predominantly occurs during April, May, and June months.
4. Meteorological Drought Hazard Mapping
4.1 Short term drought hazard mapping using SPI3
<Insert Fig. 4 here>
In the context of short-term drought assessment (SPI3), hazard mapping is conducted for specific periods, namely March, June, and September, (Fig. 4). Nevertheless, the month of December is omitted from the hazard mapping for SPI3 owing to the lack of any occurrences of drought events within the September to December timeframe. Instead, SPI3 for the time scale of March, June and September effectively captures the arid conditions experienced, thereby reflecting the precipitation patterns across distinct seasons. During the first three months of the year, the northeastern region of the state is encompassed by risk levels ranging from extreme to severe to high towards drought. This encompasses various agro-climatic zones, namely the Irrigated northwestern plains, Bikaner district within the hyper arid partially irrigated western plains, transitional plain of inland drainage, and flood-prone eastern plain. Districts that are under extremely high risk of drought occurrences are Hanumangarh, Churu, Jhunjhunu, Alwar, and Bharatpur. Both the frequency (Fig. 4a) and the severity (Fig. 4d) of drought events are high in these specific areas. The above mentioned regions exhibit a heightened susceptibility to drought in comparison to other areas of the state, primarily due to the occurrence of rainfall in the north-eastern parts during SPI3-March, attributed to western disturbances. Consequently, this specific region manifests notable rainfall variability within this temporal scale, resulting in a corresponding decline in SPI values below − 0.99. In contrast, the remaining regions within the state receive relatively diminished precipitation resulting from the influence of western disturbances, thereby demonstrating a decreased degree of variability in rainfall patterns. Thus the northeastern region, the southwestern and central part of the state is not prone to drought during these months of the year. Consequently, a significant portion (68% of the total area) of the state is characterized by a predisposition to low drought risk, while 9% area of the state falls for moderate and severe drought categories. The smallest portion of the state's territory is classified under the high and extreme drought categories, accounting for 7% of the total area respectively. The SPI3-June indicates that the central and western part of the state falls under high risk of drought compared to the other part of the state (Fig. 4). Comparatively, the western part of the state faces risk of low drought condition during this time period. Agro-climatic zones falling under the risk of extreme drought category are the Hyper arid partially irrigated eastern plain, Transitional plain of inland drainage, Semi-arid eastern plain, Sum humid southeastern plain, and Humid southern plain covering around 33% area of the state (Fig. 4h). Around 47% area of the state experience severe drought condition covering the northern and eastern districts of the state. The western zone of the state falls under the risk of high, moderate and low drought covering 8%, 8% and 4% area of the state respectively .The frequency of drought events (Fig. 4b) during SPI3-June time scale is high in the zones of the central and southern part covering the districts Bikaner, Churu, Nagaur, Ajmer, Banswara and Dungarpur of the state and the extreme severity of the drought is faced by the districts Ajmer, Pali, Rajsamand, Udaipur ,Chittorgarh, Banswara and Dungarpur. Short term hazard mapping for the month September (representing monsoon season), shows (Fig. 4i) that during this period 44% area of the state falls under the risk of High drought category. The 34% area of the state falls under the risk of severe drought like condition covering southern Arid western plain, Transitional plain of Luni basin, Humid southern plain, parts of Transitional plain of inland drainage and Flood prone eastern plain agro climatic zones. The Flood prone eastern plain agro climatic region covering district Dholpur and Bharatpur falls under the extreme drought like condition (covering 4% area of the state). The risk of Low and Moderate drought lies in the zones of Semi-arid eastern plain and Humid south eastern plain covering 2% and 16% respectively. The eastern and southern part of the state covering Dholpur, Bharatpur, Banswara and Dungarpur faces extremes in both frequency and severity category (Fig. 4c & 4f).
4.2 Medium term drought hazard mapping using SPI6
The medium-term hazard mapping reveals that the western region of the state falls relatively under low risk towards drought events during the SPI6-June timeframe (Fig. 5e). Conversely, the northern and central parts of the state are characterized by a higher prevalence of drought events. Out of all the agro climatic zones Irrigated north western plain, Hyper arid partially irrigated eastern plain and Humid southern plain along with district Ajmer falls under the risk of extreme and severe drought condition covering 12.30% and 12% area of the state respectively. During this time period the agro climatic region of south western and eastern part i.e. Ia, IIb, IIIb and V falls under low and moderate drought condition covering 12.24% and 25.75% area respectively. The remaining majority part of the state i.e. the central and eastern part of the state falls under the risk of high drought condition covering 37.71% area of the state.
The hazard mapping of SPI6-December reveals that during this particular temporal interval, the western and eastern regions, along with select pockets of southern Rajasthan encompassing the agro-climatic zones of western Ib, Ic, Ia, IIIb, eastern IVb, as well as the boundary areas of IIIa and IVa, and IIa and IIIa, are highly susceptible to severe drought conditions(Fig. 5f),. Comparatively, these areas exhibit the highest prevalence of drought, covering approximately 46.3% of the state's total area, in contrast to other regions within the state. The western part of the districts Nagaur and Kota, Bundi district is least prone region of the state falling in moderate drought like condition covering 3.9% area of the state. The mid-term drought analysis thus tells that during the first half of the year it is the northern, southern and the few pockets of central part of the state which is most prone to drought while during the second half of the year, the region prone extends to western, eastern and few pockets of the southern region of the state. During the initial half of the year, the eastern region of the state exhibits a lower susceptibility to drought. However, during the latter half of the year, the same region becomes increasingly prone to severe drought conditions.
<Insert Fig. 5 here>
4.3 Drought hazard mapping using SPI12
The long-term drought hazard map is prepared using the SPI12-December. SPI12-December depicts the overall impact of the annual variability of rainfall in the state. The hazard mapping is done using the parameters frequency, intensity and duration of the drought events.
The hazard map of drought for the state of Rajasthan indicates that the larger part of the state i.e. around 37% area of the state is prone to high drought category which is majorly scattered in the central and the eastern region of the state (Fig. 6). The zone Irrigated north western plain along with western Jodhpur district, few pockets of the flood prone eastern plain, boundary area of zones Semi-arid eastern plains and Transitional plain of inland drainage, northern part of sub humid eastern plains falls for the risk of extreme and severe drought covering 6% and 24% area of the state respectively. The Sikar district falls under the risk of extreme drought which can be attributed to the rainfall pattern over the past three decades. Analysis reveals that during the most recent decade the district has experienced a notably higher amount of rainfall compared to the preceding two decades. As the SPI methodology incorporates historical rainfall records when assessing drought conditions in a specific region, the analysis indicates that the earlier two decades were comparatively drier in contrast to the subsequent decade. The analysis here indicates that though now the Sikar district is receiving good amount of rainfall but the possibilities exists for the regions to face the low rainfall condition (similar to former two decades). The districts Barmer, Jalore, Udaipur, Banswara, western Nagaur, Kota, Bundi, Jhalawar, Sirohi and Udaipur falls for the low risk of drought events as these district receives good amount of rainfall. Around 7% area and 26% area of the state is prone to low and moderate drought respectively. Despite Jhalawar district being characterized by the highest rainfall levels within the state, it is currently facing the threat of drought due to the significant variability observed in its rainfall patterns.
The drought event occurring in the western part of the Rajasthan is more frequent and has the longer duration but the severity is not that high. The severity of drought is high in the zone of humid south eastern plain compared to the other zones covering the district Baran and Bundi. Other than this region the districts Bikaner, southern Jaisalmer, Barmer, Nagaur, Ajmer, Pali, Udaipur, Jodhpur and Sawai Madhopur faces the high severity of drought. The southern part of the state i.e. zone humid southern plains (Banswara) is facing the high frequency of the events with short duration but the severity here is high. The drought hazard map based on SPI12, illustrates that around half of the state (around 37% area) is prone to high drought category. Additionally, the moderate drought category encompasses approximately 26% of the state's area, signifying a considerable risk within these regions.
<Insert Fig. 6 here>
4 Trend Analysis of Rainfall in the state of Rajasthan
4.4.1 Trend for annual rainfall
The variability in rainfall over this state is dependent on the south west monsoon, which is a dominant land-ocean-atmospheric coupled response mechanism of temperature and pressure differences between the Indian Ocean in the south and Himalayan Mountain in the north. Recent climate change discourse (IPCC 2023) talks about the past and projected increase in temperature over the region that can impact the drought conditions of the state. The spatial pattern of mean annual rainfall in the state of Rajasthan illustrates that the average annual rainfall pattern in the western part of the Aravalli receives less rainfall compared to the eastern part of the Aravalli range (Fig. 7a). The western dry parts of Jaisalmer district receive lowest rainfall (150–300 mm) which is also the lowest in India, while the south-eastern district of Jhalawar receives rainfall in the range 900 to 1520 mm which is the highest rainfall in the state.
The results of rainfall trend analysis based on the Mann-Kendall test suggest that around 78.78% of the stations (130 out of 165 stations) are showing an increasing trend in mean annual rainfall (Fig. 7b). Rainfall trends in 26 meteorological stations (comprising 15.75%) have shown significant increases at different significance levels (Table 4). These stations well are scattered across the state and mostly found over the Aravalli range. The trend results of the study is in line with the previous studies of Saini et al. (2022); Meena et al. (2019) and Lal et al. (2001) where they also found significant increasing trends of mean annual rainfall in Churu, Pratapgarh, and Jaisalmer stations. Negative trends are found in 20.60% stations (34 out of 165 stations) among which only two stations experienced significant negative trend (Tapukara and Nadbai in Alwar and Bharatpur districts respectively) that are mainly found in the north-eastern parts of the state.
Table 4
Trend of mean annual rainfall
|
Stations
|
Test Z
|
Sen’s slope estimate(mm/yr)
|
Stations
|
Test Z
|
Sen’s slope estimate(mm/yr)
|
|
ASIND
|
2.80**
|
6.26
|
NEEMKATHANA
|
3.02**
|
10.9
|
|
BASERI
|
3.02**
|
11.94
|
PHALODI
|
2.31*
|
4.3
|
|
BIKANER
|
2.34*
|
4.63
|
PISANGAN
|
2.56*
|
8.73
|
|
BILARA
|
2.03*
|
5.13
|
POKARAN
|
2.12*
|
5.36
|
|
CHAKSU
|
2.22*
|
7.4
|
PRATAPGARH
|
3.22**
|
19.85
|
|
DEWAL
|
3.46***
|
13.62
|
PUSHKAR
|
2.25*
|
8.33
|
|
DIDWANA
|
3.38***
|
9.92
|
RAJJGARH©
|
3.05**
|
7.96
|
|
FATEHGARH
|
2.18*
|
4.19
|
RAJSAMAND
|
2.13*
|
7.29
|
|
FATEHPUR
|
2.31*
|
7.2
|
RAMGARH
|
3.53***
|
14.48
|
|
GIRWA
|
2.05*
|
7.5
|
SARARA
|
2.11*
|
5.36
|
|
HINDOLI
|
2.34*
|
8.83
|
SAWAIMADOPHAR
|
2.31*
|
14.33
|
|
MERTACITY
|
2.76**
|
8.83
|
SRIMADOPHAR
|
2.03*
|
10
|
|
NAINWA
|
3.04**
|
11.85
|
NADBAI
|
-2.13*
|
-6.97
|
|
NATHDWARA
|
2.06*
|
7.37
|
TAPUKARA
|
-3.85***
|
-12
|
|
Significant at 0.001***, 0.01** level and 0.05* level
|
Interestingly, it is noteworthy here that the western region in the Marusthali desert area of the state, exhibits a concurrent rise in the annual average precipitation, which is also mentioned in study of Kumar et al. (2010). Interestingly few stations of the eastern part of the state are showing the decreasing trend of the mean annual rainfall which is indistinguishable with the study of Mundetia and Sharma (2015); Mondal et al. (2015); Kumar et al. (2010). The study of Lal et al. (2001) has also mentioned that the arid western part of the state soon coming could receive higher rainfall because of the warming climate.
<Insert Fig. 7 here>
<Insert Table 4 here>
The trend pattern of drought event occurrences across various stations reveals that the majority of stations exhibited a declining trend during the specified time periods (Fig. 8). This can be attributed to the increase in rainfall which aligns with the study of Saini et al. (2022) which highlighted a non-significant increase in rainfall during the winter, pre-monsoon, and monsoon seasons in Rajasthan. During the months of January to March (as shown in the figure), the majority of stations (58.78%) displayed as such no trend of drought event occurrences. However, 16.36% of the stations exhibited an increasing tendency, while 24.84% displayed a decreasing trend in drought occurrences. Notably, the stations indicating a decreasing trend were primarily located in the eastern region of the state, encompassing districts such as Bikaner, Sikar, Alwar, Bharatpur, and northern Ganganagar. Moreover, the Tapukara station in Alwar exhibited a significant increase in drought events, whereas the Bonli station in Sawai Madhopur and the Manoharthana station demonstrated a significant decrease in drought occurrences at a 95% significance level.
During the pre-monsoon period, specifically from April to June, approximately 21.21% of the stations exhibited an increasing trend in drought event occurrences. The majority of these stations were situated in the southern region of the state. Around 4.24% of the total stations displayed no discernible trend in drought event occurrences. Conversely, approximately 74.54% of the stations demonstrated a decreasing trend in drought occurrences, distributed across various locations within the state. Significant decreasing trends in drought event occurrences were observed at several stations, namely Didwana, Jodhpur, Pokaran, Nadoti, Dewal, Lunkarnsar, Behrod, Sawaimadhopur, Fatehgarh, Ganagapurcity, Khandar, Bikaner, Srimathura, Neem ka thana, and Ramgarh(Sikar).
During the monsoon period, specifically from July to September, 25.45% of the stations displayed an increasing trend in drought occurrences. The majority of these stations were scattered across the eastern part of the state. Additionally, in accordance with the findings of Saini et al. (2022), the westernmost region of the state also experienced a reduction in rainfall. Among all stations; Tapukara (Alwar) exhibited a significant increase in drought event occurrences. 74.54% of the stations demonstrated a decreasing trend in drought occurrences. Notably, six stations (as shown in Fig. 8) exhibited a statistically significant decrease in drought-like conditions. These stations include Nainwa, Baseri, Didwana, Pratapgarh, Ramgarh(Sikar), and Dewal.
The analysis of SPI66 reveals that during the period from January to June, the majority of station (80.60% of the total), experienced a decrease in drought event occurrences (Fig. 8). Among them, 15 stations exhibited a significant decreasing trend, namely Ratangarh, Deeg, Hindon, Neem ka thana, Srimathura, Khandar, Pokaran, Sepau, Sawaimadhopur, Fatehgarh, Ganagapurcity, Didwana, Baseri, Rajgarh(churu), and Ramgarh(Sikar). Conversely, 19.39% of the stations displayed an increasing trend in drought events, with Tapukara being the only station showing a statistically significant increasing trend. Moving to the second half of the year, from July to December; approximately 25.45% of the stations exhibited an increasing trend in drought event occurrences, while 74.54% of the stations demonstrated a decreasing trend. Notably, Tapukara and Sam stations displayed a significant increasing trend, whereas Asind, Nimbhahera, Nainwa, Pratapgarh, Baseri, Didwana, Ramgarh(Sikar), and Dewal stations exhibited a significant decreasing trend during this period.
Similarly, while examining the SPI12 for December, a similar trend emerges. The majority of stations, accounting for approximately 79.39% of the total, displayed a decreasing trend in drought occurrences. Conversely, 20.60% of the stations exhibited an increasing trend. Notably, Tapukara and Sam stations demonstrated a significant decrease in drought events, while stations including Bundi, Mertacity, Sarara, Fatehpur, Asind, Nimbhahera, Bikaner, Neem ka thana, Rajgarh(Churu), Sawaimadhopur, Pratapgarh, Baseri, Nainwa, Didwana, Ramgarh(Sikar), and Dewal showed a significant increasing trend.
Furthermore, it is evident from the trend analysis across various time scales that there is a distinct geographical pattern in the trend pattern of occurrence of drought events. During the initial three months, the northern and northeastern regions of the state exhibit an upward trend in drought occurrences. As the months progress, the risk of drought shifts to the southern areas of the state. However, during the July to September period, the northeastern and westernmost parts of the state experience resurgence in the frequency of drought events. This consistent trend pattern can be observed in the SPI3-September, SPI6-December, and SPI12-December analyses, underscoring the significance of the rainfall during the July to September period in shaping the overall trend pattern in the state.
Overall, the findings highlight the vulnerability of the Alwar district and the westernmost region of Jaisalmer to an increasing pattern of drought event occurrences. Understanding these regional dynamics is crucial for effective drought management and resource allocation in the state.
<Insert Fig. 8 here>
<Insert Table 5 here>
Table 5
Trend of SPI3 values for different time scale
|
SPI3 March
|
SPI3 June
|
SPI3 September
|
|
Stations
|
Z test
|
Sen’s slope estimate(mm/yr)
|
Stations
|
Z test
|
Sen’s
slope estimate (mm/yr)
|
Stations
|
Z test
|
Sen’s slope estimate
|
|
Begun
|
2.02*
|
0.004
|
Tonk
|
2.19*
|
0.027
|
Tapukara
|
-3.47***
|
-0.054
|
|
Pisangan
|
2.37*
|
0.006
|
Jodhpur
|
2.07*
|
0.033
|
Nokh
|
2.03*
|
0.033
|
|
Bonli
|
2.43*
|
0.023
|
Didwana
|
2.28*
|
0.037
|
Asind
|
2.12*
|
0.034
|
| |
|
|
Nagar
|
2.25*
|
0.036
|
Neem ka thana
|
1.97*
|
0.037
|
| |
|
|
Lunkansar
|
2.24*
|
0.037
|
Mertacity
|
2.27*
|
0.042
|
| |
|
|
Deeg
|
2.40*
|
0.037
|
Baseri
|
2.36*
|
0.044
|
| |
|
|
Fatehpur
|
2.05*
|
0.037
|
Phalodi
|
2.21*
|
0.044
|
| |
|
|
Baseri
|
2.31*
|
0.038
|
Nainwa
|
2.27*
|
0.045
|
| |
|
|
Rashmi
|
2.12*
|
0.038
|
Pratapgarh
|
3.04**
|
0.049
|
| |
|
|
Behrod
|
2.25*
|
0.039
|
Didwana
|
2.86**
|
0.053
|
| |
|
|
Ratangarh
|
2.05*
|
0.039
|
Dewal
|
2.77**
|
0.055
|
| |
|
|
Pokaran
|
2.40*
|
0.04
|
Ramgarh(sik)
|
2.95**
|
0.056
|
| |
|
|
Bilara
|
2.02*
|
0.04
|
|
|
|
| |
|
|
Khandar
|
2.28*
|
0.040
|
|
|
|
| |
|
|
Ganagapurcity
|
2.40*
|
0.041
|
|
|
|
| |
|
|
Srimathura
|
2.40*
|
0.042
|
|
|
|
| |
|
|
Taranagar
|
2.62**
|
0.042
|
|
|
|
| |
|
|
Nadoti
|
2.40*
|
0.043
|
|
|
|
| |
|
|
RajgarhC
|
2.03*
|
0.045
|
|
|
|
| |
|
|
Fatehgarh
|
3.20**
|
0.047
|
|
|
|
| |
|
|
Neem ka thana
|
3.08**
|
0.054
|
|
|
|
| |
|
|
Ramgarh(sik)
|
3.41***
|
0.061
|
|
|
|
|
Significant at 0.001***, 0.01** level and 0.05* level
|
<Insert Table 6 here>
Table 6
Historical drought year and identified drought year (1988–2021) for specific meteorological stations of Rajasthan
|
Stations
|
District
|
Lowest rainfall*
|
Lowest Annual rainfall as % of normal years
|
SPI based drought year(Present study)
|
Lowest SPI value
|
Accuracy (%)
|
|
Ahore
|
Jalore
|
1991
|
26
|
1991
|
-2.31
|
100
|
|
Bamanwas
|
Sawaimahopur
|
1989
|
49
|
1989
|
-2.73
|
100
|
|
Baseri
|
Dholpur
|
1989
|
30
|
1989
|
-2.35
|
100
|
|
Chirawa
|
Jhunjhunu
|
1989
|
41
|
1989
|
-2.58
|
100
|
|
Didwana
|
Nagaur
|
1989
|
39
|
1989
|
-1.77
|
100
|
|
Gangapur City
|
Sawaimadopur
|
1989
|
29
|
1989
|
-2.83
|
100
|
|
Khandar
|
Sawaimadopur
|
1989
|
35
|
1989
|
-2.57
|
100
|
|
Lachmangarh
|
Alwar
|
1989
|
44
|
1989
|
-2
|
100
|
|
Nadoti
|
Karoli
|
1989
|
33
|
1989
|
-2.22
|
100
|
|
Nagar
|
Bharatpur
|
1991
|
36
|
1991
|
-2.2
|
100
|
|
Nainwa
|
Bundi
|
1989
|
30
|
1989
|
-2.4
|
100
|
|
Nokha
|
Bikaner
|
1991
|
26
|
1991
|
-2.62
|
100
|
|
Phalodi
|
Jodhpur
|
1991
|
22
|
1991
|
-2.12
|
100
|
|
Pipalda
|
Kota
|
1989
|
46
|
1989
|
-1.66
|
100
|
|
Pushkar
|
Ajmer
|
1991
|
7
|
1991
|
-3.45
|
100
|
|
Ratangarh
|
Churu
|
1991
|
32
|
1991
|
-1.91
|
100
|
|
Sapotara
|
Karoli
|
1989
|
44
|
1989
|
-1.88
|
100
|
|
Talera
|
Bundi
|
1991
|
23
|
1991
|
-3.06
|
100
|
|
Karanpur
|
Ganganagar
|
1991
|
35
|
2000
|
-2.25
|
0
|
|
Padampur
|
Ganganagar
|
1991
|
31
|
2002
|
-2.35
|
0
|
|
Sallopat
|
Bansawra
|
1991
|
46
|
1991
|
-1.72
|
100
|
|
Bayana
|
Bharatpur
|
1991
|
64
|
2002
|
-2.03
|
0
|
|
Sahada
|
Bhilwara
|
1993
|
45
|
1993
|
-2.21
|
100
|
|
Rashmi
|
Chittorgarh
|
1993
|
45
|
1993
|
-2.29
|
100
|
|
Karoli
|
Karoli
|
1991
|
53
|
2002
|
-2.17
|
0
|
|
Total Accuracy = 84%
|
|
*Historical year with Lowest rainfall (according to IMD, Pune)
|
Based on the findings of the study, several significant characteristics of drought events in the state of Rajasthan can be summarized. The investigation of the SPI across 165 meteorological stations during the time span of 1988–2021 revealed that periodic occurrences of extremely negative SPI values were recorded across all stations. These observations were cross-referenced with the historical lowest rainfall data reported by the India Meteorological Department (IMD) Pune report of 2010 ( https://imdpune.gov.in/library/public/Climate%20of%20Rajashtan.pdf ). This report documented the years with the lowest recorded rainfall based on the available data until the year 2006. Notably, the report specified the lowest rainfall records for 25 out of the 164 meteorological stations considered in this study. Thus the study tried to closely align the calculated SPI value of these 25 stations with the historical year records of rainfall provided in the report. Notably, the findings of the study closely align with the historical data of the report (Table 6). It is thus evident that several of the driest episodes could be discerned based on the SPI values. Consequently, it can be concluded that SPI values hold potential for identifying drought events within specific regions and across the state of Rajasthan.
4.6 Conclusion
The accurate identification and understanding of different levels of dryness across different time frames hold significant importance in understanding and conducting seasonal drought analysis. Here we studied the rainfall and drought characteristics during the observation period of 1988–2021 over the Indian state of Rajasthan to identify the drought hazard-prone areas. Spatial-temporal analysis of drought hazard is done by combining the frequency, severity, and duration of drought events which is crucial for short and long-term drought management strategies. The spatial pattern indicates that severe drought majorly occurs during the months of July - September while moderate and mild droughts are more common during the months of April - June. We also found that the likelihood of extreme drought conditions occurring in the state is relatively low and the state does not experience extreme drought events during the months of October to March. The study reveals that the distribution of drought-prone areas within the state varies with season. During January to March, the northeastern part of the state is most susceptible to drought events. In the following three months (i.e., April to June), the central and southern districts of the state face a higher risk of drought. However, during July to September, drought-prone regions are primarily concentrated in the western and northeastern parts of the state. This suggests that drought vulnerability within the state of Rajasthan exhibits a seasonal pattern, wherein various regions face elevated risks of drought at different periods throughout the year. The analysis of medium-term drought (SPI6) suggests that the occurrence of drought events during the first half of the year (January to June) is relatively lower compared to the second half. Additionally, the study also explored the trend patterns in historical rainfall and drought events, using the Mann-Kendall and Sen's slope methods. The findings reveal an overall increase in rainfall across most of the stations in Rajasthan, indicating an overall positive trend in mean annual rainfall. However, the northeastern part of the region, encompassing districts such as Alwar, northern Jaipur, and western Bharatpur and Dausa, shows an exception to this trend and showed negative trends in rainfall. In response to the increase in rainfall, drought events are found to decrease over the state at shorter as well as longer time scales.
The long-term drought hazard map prepared using the SPI12-December depicts the overall impact of the annual variability of rainfall in the state. Based on this we noted that the districts Sriganganagar, Hanumangarh, Jaislamer, Jodhpur, Sikar,, Western Bikaner and the eastern Jaipur are the most prone to drought in Rajasthan. Conversely, the districts lying in the southwestern and the eastern part of the state are less prone to drought. Our findings also reveal that milder drought events are most frequent in the northern region of the state. Moderate events, on the other hand, are more dispersed throughout the entire state except central Rajasthan. While the occurrence of extreme drought events predominantly occur in the western, northern, and central part of the state.
The comprehensive drought hazard maps prepared through this study, encompassing various time scales, offer a practical tool for identifying and demarcating drought-prone areas. The prepared hazard maps of SPI3-June and September could be useful in understanding the impact of rainfall variability over kharif crops while the SPI3-March is important for rabi crops. This delineation provides valuable insights for policymakers when making decisions related to agriculture, regional hydrological plans, and sustainable development goals in the region. Furthermore, this mapping technique can be easily adapted and applied to other regions susceptible to drought, even with limited data availability.