Socioeconomic losses during Dust events of May 2018
The devastating dust storm in northern parts of India especially, Uttar Pradesh, Bihar, Delhi, and Rajasthan in May 2018 is listed among 35 extreme weather events caused by the climate changed, mentioned in ‘The Global Climate in 2015–2019’ report released by the WMO. The first, deadly severe dust storm (claimed more than 125 deaths and over 200 injuries) hit India's northern states on 2–3 May 2018. Subsequently, the second (7–8 May 2018) and third (12–13 May 2018) dust storm have reported fewer socioeconomic annihilation and casualties. SDS affect the different segments of an economy, either directly (immediate consequences of events) or indirectly (secondary outcomes that may occur after direct effects) (Al-Hemoud et al., 2019). As, the direct effects consider detrimental health consequences, human and livestock causalities/deaths, road accidents, airline delays/diversions/cancellations, uprooting of trees and crops, damages of residential premises, and electrical house/poles.
As per available record from the different airbases of northern parts of India during May 2018, more than 70 flights were diverted, and dozens of flights were delayed. On the other hand, state governments had declared 5,642 USD (400,000 INR) will be given to family members of deceased, and around 2,821 USD (~ 200,000 INR) to persons sustaining 40–60 % injuries. In order to evaluate gross economic loss to airlines, the breakdown charges for different segments of flight operations was obtained from the Center for Asia Pacific Aviation (CAPA) of India and Indian Civil Aviation Ministry (Kulkarni et al., 2019). Therefore, based on the abovementioned information and records, the cumulative losses have been evaluated. Here, the diversion and delay of flights collectively caused an economic loss of approximately 0.55 million USD (36.86 million INR). However, the cumulative losses in terms of the impediment in airline operations (delay and diversion), live casualties and deaths have been estimated at US$1.3 million (86.75 million INR), over these dust episodes. Particularly, this estimated loss based on these two aspects are approximately equal to 1–2% of the total destruction cost that occurred due to dust episodes in May 2018 in the northern part of India.
Prevailing Meteorology during Dust events of May 2018
Figure 2 showed, the satellite images of these dust plumes persisting over the IGP region which have been retrieved from NASA Earth Observing System MODIS-Terra platform (https://worldview.earthdata.nasa.gov) for 02 May, 07 May, and 13 May in 2018, respectively. Moreover, the spatial sweep of dust carried from Pakistan, the Arabian Peninsula, and the Thar Desert has been clearly depicted in Sarkar et al., 2019. Even if this dust plumes are not seen thick enough in satellite images but it has deteriorated the air quality of urban and rural areas drastically. In order to reconfirm these dust events, hourly averaged diurnal variation of particulate matters along with the influential surface meteorological drivers have been examined, which is represented in Fig. 3.
First intense dust storm DS1 (represent by the shaded patch) hit the observational site on 02 May 2018 around 17:00 − 18:00 LST, resulting in a significant increase in PM concentration. From Fig. 3(a), first peak (DS1) of PM10 (PM2.5) concentration at IGI airport suddenly increased (~ 4 times) from 138 (55) µg m− 3 at 16:00 − 17:00 LST to 528 (106) µg m− 3 at 17:00 − 18:00 LST. Subsequently, during the second (DS2) and third dust storms (DS3), gradually increased in PM10 (PM2.5) concentration from 354 (96) µg m− 3 at 22:00 LST to 776 (101) µg m− 3 at 23:00 LST on 07 May 2018, and 182 (79) µg m− 3 at 15:00 LST to 335 (80) µg m− 3 at 16:00 LST on 13 May 2018. Similar kind of sharp peaks in particulate matter mass concentrations (2 − 50 times of its control values) within the short periods have been noticed over the Gobi Desert by Jugder et al. (2014) and Kawai et al. (2019). Succinctly, an abrupt rise in given particulate matter concentrations, indicates the potency of these dust storms.
Frequently, the PBLH extend up to 2 − 3 km over the northern part of the Indian subcontinent during the summertime period as a result of intense solar heating (Patil et al., 2013). Nevertheless, Fig. 3(a) clearly demonstrate, the uplift and vertical extent of dust mainly influenced by the surface meteorology within the atmospheric boundary layer which could stretch PBLH above 3km. Moreover, the diurnal variation of PBL is the response of radiation, winds and energy balance. In the early mornings (05:30 LST), the stable boundary layers at calm wind condition persisted below 500 m AGL. In contrast, convective boundary layer heights around late afternoons (17:30 LST) ranged between 1000 m AGL and 3800 m AGL, pointing toward colossal vertical mixing. Meanwhile, prior to each dust storms, a dry atmospheric agreement lower atmosphere has been noticed which is conclude from 20 − 30 % reduction in RH values during maximum temperature range (Fig. 3(b)). On the other hand, convective instability is built up during each dust events through an increase in low level moisture (by 30 − 40 %) corresponding to rapid fall down in temperature (about 10 K) in 6 hours of interval. In addition, a sudden shift in wind vector shown in Fig. 3(c), has conferred to vertical dust mixing/turbulent activities.
However, these suddenly impacted dust storms directly affected the radiative fluxes which could be clearly analysed by comparing it’s diurnal variations obtained a day prior to dust storm (Solid line), during the dust storm (Symbolic line), and the day after the dust storm (Dash line) reported in Fig. 4. Generally, in most of the dust storm cases worldwide, it has been observed that longwave flux (includes both Incoming and Outgoing) values one day before (one day after) dust activity are high (less) as noticed in DS2 and DS3 event depicted in Fig. 4(a) and Fig. 4(b). Interestingly, the opposite result seems in the case of DS1, where dust day shows trivial raised in longwave fluxes compared to the former day. Concisely, the sudden subsidence of non-local dust over NCR, Delhi without a prior day warming, could be a reason for that. The gradually increased diurnal values of longwave flux before each dust episodes show additional radiative energy has caused a warming of the lower atmosphere. Afterwards, the Incoming longwave flux; significantly decrease from its peak within an hour during DS1 (from 468 to 439 W m− 2), DS2 (from 470 to 448 W m− 2), and DS3 (from 495 to 450 W m− 2). Additionally, such rapid fall in the percentage of Outgoing longwave flux (6%, 5%, and 10%) along with minor cut off in shortwave fluxes (includes both Incoming and Reflected) due to these huge dust intrusion in a short time could yield the cool next hours/days relative to preceding warmer hours/days. The increased daily mean of surface temperature (by 4–5 K within 15 days dust span), stepped up (stepped down) diurnal cycles of longwave fluxes (shortwave fluxes) from DS1 to DS3 are utter pinpoints that after each consecutive dust activities, the inclusion of dust aerosols has loaded in FT.
However, in order to reveal these meteorological and radiative features associated with dust activities in pictorial form, the ceilometer backscatter profiles have been combined and analysed for the same dust span. Figure 5, shows the time-height cross-section of the ceilometer aerosol ABC in m− 1 sr− 1 from 01 May 2018 to 16 May 2018. In that, green and brown shades represent aerosol top layers and cloud bottom layers. From the ceilometer backscatter profile it has been disclosed that the residual dust layers after each dust episodes (DS1, DS2, and DS3) were extended vertically to the FT. For evidence, the small angstrom exponent corresponding to higher Aerosol Optical Depth at 550 nm (AOD550) indicated a significant increase in aerosol loading, especially in the coarse mode in FT (D. Lal et al., 2018; Sarkar et al., 2019). Often, after the dust episodes the elevated columnar water vapour in the upper troposphere has been observed which further leads to cause the thunderstorms/rainy activities over IGP and part of northwest India (Dey et al., 2004; Prasad and Singh, 2007a, 2007b). These events are usually short and sporadic. Likewise, four scatter rainfall events RF1 (2.5 mm), RF2 (0.2 mm), RF3 (1.6 mm), and RF4 (6.7 mm) at IGI airport has been recorded. Particularly, the rainfalls after DS1 and DS3 event are associated with WDs which bring ample amount of moisture and maintain low level clouds, especially over NCR which are depicted in Fig. 2(a), Fig. 2(c) and Fig. 5. Additionally, it has been noticed in ceilometer backscatter profile that the RE4 after DS3 was relatively strong enough to washout floating dust and pollution in the atmosphere which was specifically persisted in FT after DS1. By considering comprehensive facts of all dust episodes in terms of socioeconomic impact, prevailing meteorology, and direct and indirect repercussion of radiative fluxes, the detailed analysis of DS1 has been carried out.
Vertical dust distribution and its peculiarities - Before Dust Storm (DS1)
Time-height cross section of ceilometer backscatter profile and surface meteorological observations at IGI airport illustrated in Fig. 6 for thorough analysis of DS1. In addition, Table 1demonstrates the variations in half-hourly averaged ABC values within two vertical heights (0–0.5 km and 0.5–1 km) corresponding to prior, during, and after the dust storms and posterior to rain events, respectively. Similarly, for the same time variations in half-hourly averaged vertical attenuated backscatter profiles for the DS1 event represented in Fig. 7.
The residual aerosol layer between 2–3 km height and low aerosol concentrations in FT during a stable night period has represented in Fig. 6(a). However, the aerosol backscatter signals, wind speed, and the temperature gradually increased in morning hours (06:00 LST) of DS1 event. During this cloud-free daytime, the maximum hourly averaged temperature of 36.37℃ is recorded 1 hr before the DS1 (between 16:00 LST to 17:00 LST), indicates the local convection. Therefore, the depth of aerosols layers nearly 1–2 km in the daytime period, is mainly influenced by local convective instability and turbulent venture. This turbulence in the mixed layer is convectively driven.
Moreover, in Fig. 6, the vertical ceilometer backscatter profile shows the turbulent activity is more dominant within 1 km before the dust storm event. From Table 1 and Fig. 7, it has also been noticed that the half-hourly averaged ABC value from 16:10–16:40 LST (20 min before DS1) within 0.5 km of the boundary layer (0.73 × 10− 6 m− 1 sr− 1) recorded slightly less than ABC value (0.80 × 10− 6 m− 1 sr− 1) within 0.5–1 km. During the clear day, unstable conditions might have created strong winds and vertical convection, which created the vertical aerosol mixing. However, these unstable conditions and convective eddies during the daytime period cause non-local transport above the mixed layer. The gradually increasing scattered vertical backscatter profile (black line) after 2 km also shows the non-local dust transport over the IGI airport.
Table 1
Variations in half-hourly averaged attenuated backscatter coefficient on 02 May 2018 corresponding to prior, during, and posterior of the dust storm and after a rainfall event within 0–0.5 km and 0.5–1 km height.
Dust Activity
|
Attenuated Backscatter coefficient in m− 1 sr− 1
|
0–0.5 km
|
0.5–1 km
|
Before DS1 (16:10–16:40 LST)
|
0.73 × 10− 6
|
0.80 × 10− 6
|
During DS1 (17:00–17:30 LST)
|
5.63 × 10− 6
|
0.45 × 10− 6
|
After DS1 (17:30–18:00 LST)
|
2.40 × 10− 6
|
0.64 × 10− 6
|
After Rain (20:30–21:00 LST)
|
0.28 × 10− 6
|
0.16 × 10− 6
|
Vertical dust distribution and its peculiarities - During Dust Storm (DS1)
Several stability indices such as Convective Available Potential Energy (CAPE), Lifted Index (LI), Severe Weather Threat Index (SWEAT) based on radiosonde data during the 02 May 2018 dust storm (17:30 LST) have calculated from the Radiosonde profile. Maximum values of CAPE (2696 J kg− 1) and SWEAT (406.39) along with highly negative lifted index (– 8.98), indicates a strong convective forcing and thermal turbulence over New Delhi during DS1. On the same day, after recording the maximum temperature at 16:00 LST over the IGI airport, continuously dropping surface temperature over 6 hrs of period indicates radiative cooling at the surface. In two hours (from 16:00 LST to 18:00 LST), the surface temperature dropped by 6.2 K. Meanwhile, the significantly high ABC value (5.6 × 10− 6 m− 1 sr− 1) represent intense dust activity within 0.5 km from 17:00 LST to 17:30 LST due to the convective activity. However, the small ABC value (0.45 × 10− 6 m− 1 sr− 1) between 0.5 − 1 km heights represents the shallow dust layer during the same period. From Fig. 7, the vertical backscatter profiles difference between prior (black line) and during (red line) DS1 demonstrates positive values, especially above 0.5 km. Also that, sharply decreasing vertical backscatter profiles (shown in Fig. 7 by a red line) comparing with increasing vertical relative humidity (shown in Fig. 8(a) by a blue line) up to 1 − 1.5 km during DS1 indicates frequently wet deposition of the upper-level dust in the lower level.
The half-hourly average ABC value within a height of 0.5 km increased by about 7.3 times over 1 min from 17:00 LST to 17:01 LST. In this case, the ABC values within 0.5 km height suddenly increased over a few min of intervals. Also, the sharp dropdown in ABC within 0.5–1 km height shows the sudden impact of developed dust storms at IGI airport, Delhi. However, this dust storm is developed somewhere before reaching to the observational site. A similar result was noticed by Kawai et al. (2019) during the ceilometer observation of dust event in the Gobi Desert on 29–30 April 2015. We also noticed a positive relation between a dust storm and wind speed like the previous study by Kawai et al., 2019. The hourly averaged wind speed recorded 6 − 8 m s− 1, and the wind direction suddenly rotated from southwest to northeast during DS1.
Vertical dust distribution and its peculiarities - After Dust Storm (DS1)
The surface wind speed is rapidly turbulent (8–9 m s− 1), which enhanced the dust mixing in the boundary layer and reduce its concentration at the surface. The half-hourly averaged ABC value recorded at the surface just after dust storm (2.40 × 10− 6 m− 1 sr− 1) was 2.34 times less compare to ABC during a dust storm (5.63 × 10− 6 m− 1 sr− 1). However, the values within the height of 0.5–1 km slightly increased (0.45 × 10− 6 – 0.64 × 10− 6 m− 1 sr− 1) over half an hour from 17:30 LST to 18:00 LST on 02 May 2018. This ABC values corresponding to the dust was relatively increased above 0.5 km height, indicating the strong vertical mixing. Therefore, ascending air should have updraft dust particles and extend it nearly 3–4 km high from the dust storm to the floating dust layer's height. The vertical structure of this floating dust layer (extended almost 4 km) represented in Fig. 7 (green line) shows more dust concentration than the DS1 period (red line) above 0.5 km height. However, from the ceilometer backscatter profile depicted in Fig. 5 the height of this floating dust layer persisted almost unchanged for the next 34 hrs.
Meanwhile, the floating dust layer reached the FT and mixed with clouds. From 10 km ceilometer backscatter profile (not given here), it is observed that cloud base height decreased from 8 km at 17:40 LST to 2 km at 19:00 LST. Later, two scatter rainfall events viz. RE1 and RE2 were recorded after the dust storm DS1. The RE1 and RE2 occurred within intervals of 2 hrs and 34 hrs from the dust storm period. These two scatter rainfall results from the western disturbances, floating dust layer and its interaction with cloud, which is clearly depicted in Fig. 2 and Fig. 5. Also, Kawai et al. (2018; 2019) noticed the same results of floating dust layer mixing with clouds after the dust events in the ceilometer backscatter profile. Rain, cloud base and cloud depth are represented by large ABC value (> 9.0 × 10− 6 m− 1 sr− 1). Figure 6(a) and 6(c), illustrates the onset of first scatter rainfall RE1 noticed after DS1which started to precipitate (0.9 mm hr− 1) at 19:40 LST and its peak (2.5 mm hr− 1) at 20:30 LST on 02 May 2018. Gusty winds, cloudy conditions, and scatter rains led to a significant drop in the ambient temperature by 4–5 K within 2 hrs (19:00 LST – 21:00 LST).
Vertical dust distribution and its peculiarities - After Rain
In a period of 03:30 hrs (between red and blue profiles), the ABC values underneath of 0.5 km sharply reduced by 20 times to dust time ABC values (5.63 × 10− 6 m− 1 sr− 1 to 0.28 × 10− 6 m− 1 sr− 1).
After the scatter rainfall RE1, the ABC values (blue line, less than 0.5 × 10− 6 m− 1 sr− 1) became lower than dust event values (red line) below 1 km height. Meanwhile, the primary pollutant namely, PM10 (PM2.5) mass concentrations recorded 108 µg m− 3 (17 µg m− 3) between 20:00 LST and 21:00 LST shows a drastic improvement in air quality. Surprisingly, raised ABC values in blue profile above 1 km represents that floating dust load was still remained above 1 km of lower atmosphere. However, the floating dust around the height of 3–4 km AGL was persisted almost for 34 hrs from the time of DS1 depicted in Fig. 5. The horizontal spike (higher ABC values) in blue profile above 4 resulted from high response of ABC to low level moist clouds which cross verified from cloud base height of ceilometer product. Therefore, the presence moist low level clouds trapped floating dust underneath of 4 km height and avoided to extend it into the FT. The secondary shallow dust layer formed underneath of floating dust layer correspond to different dust source after 9 hrs intervals of RE1. This lower sub dust layer within 1 km is generated from the local dust pollutants, while the overhead floating dust layer within 4 km was residual part of the dust storm DS1.
From the radiosonde profile at 05:30 LST on 03 May 2018 shown in Fig. 8(b), the number of interesting facts has been noticed. In particular, (1) the strong inversion (ground level values missing up to 200 m) of 6.8 ℃ under the potential temperature gradient of 19.67 K km− 1 (11.8 K in a height range of 0.6 km) in calm wind condition indicates diminutive convection (high atmospheric static stability) and feeble thermal turbulence within 0.8 km (close to 900 mb), (2) reducing values of relative humidity in vertical profile (from 68 % to 24 %) under the inversion layer depth perfectly signifying the dry warmer air is held above cold surface, (3) Sharpe turn in temperature gradient and relative humidity profile above the inversion layer, trapped dust aerosols within 1 km which exactly depicted in Fig. 5 as a sub dust layer, and (4) the inclusion of the moist air advection underneath of 4 km height have been noticed from the vertical profiles of RH (increased around 60 % above inversion layer) and potential temperature. However, very steep variation vertically in ABC (blue line in Fig. 7) from 4 km AGL to 5.5 km AGL could result of low cloud. Ultimately, it cloud be acknowledge that floating dust layers (sub dust layer) has been trapped under low-level clouds (inversion layer) and persisted at almost the same height for 34 hrs (23 hrs).