3.2 Analyzing the projected precipitation
3.2.1 Projected changes in annual average precipitation in 2021–2040
Under four shared socioeconomic pathways (SSPs), the changes in average annual precipitation over Bangladesh between the base line period and the duration 2021–20240 have been presented in Fig. 4. The changes in projected precipitation in 2021–2040 are noted as positive in the north-east and south-east areas of Bangladesh, which reveals the increase in precipitation compared to the base line period. Considering these precipitation changes on a division basis, it is found that the projected precipitation has been increased greatly in the south-east regions of the Chittagong division under all SSPs, except SSP5.85. The precipitation is found there to be increased by 1000 to 1600 mm. While the projected precipitation in the Sylhet division has moderately increased, particularly under SSP 1.26 with the magnitude of 600–1400 mm. A very large portion of Bangladesh, such as the entire Barisal division, substantial parts of Chittagong and Rangpur, and under some SSPs, Khulna and Dhaka, will have received slightly more precipitation than the base line period precipitation that could be ranged between 0 to 400 mm. However, the projected precipitation alarmingly decreased in the Dhaka division and Rajshahi divisions under the SSP 2.45 and SSP 5.85. Under SSP5.85, the entire Khulna and Rajshahi divisions are found to have decreased precipitation by 200–521 mm, while the highest precipitation decrease is noticed in the Dhaka division under SSP5.85 and followed by SSP2.45.
3.2.2 Projected changes in annual average projected maximum and minimum precipitation in 2021–2040
In Chittagong, Sylhet, Rangpur, and Barisal, it is seen (Fig. 5) that the predicted change in maximum precipitation is found positive for all SSPs, indicating an increase in precipitation relative to the baseline. On the other side, Khulna division is observed to have negative maximum precipitation for all SSPs. Precipitation variations are recorded in both beneficial and bad ways for Rajshahi and Dhaka. Positive precipitation was seen in Rajshahi under SSP1.26 and SSP2.45, and in Dhaka under SSP1.26 and SSP3.70. In contrast, Dhaka saw negative precipitation under SSP2.45 and SSP5.85. In contrast, negative precipitation was found in Dhaka under SSP2.45and SSP5.85. In this projection period the height increase in maximum precipitation of 1518 mm is obtained in Chittagong under SSP2.45, while height decrease in maximum precipitation of 429 mm is obtained in Khulna under SSP5.85. In Chittagong, with SSP 2.45, the maximum precipitation increased by 1518 mm over this projected period, however in Khulna, under SSP 5.85, the maximum precipitation decreased by 429 mm during this time.
The expected change in annual average minimum precipitation is only positive in Barisal among all divisions, whereas negative changes are seen in Rajshahi and Rangpur under all SSPs. The remaining four categories offer a combined total of both the adverse and favorable changes in precipitation. Under SSP1.26, however, the height positive changes in minimum precipitation are obtained at 396 mm in Barisal, while the height negative changes in minimum precipitation are obtained at 216 mm in Sylhet (Fig. 6).
3.2.2 Projected changes in annual average precipitation in 2041–2060
Under four shared socioeconomic pathways (SSPs), the changes in average annual precipitation over Bangladesh between the base line period and the duration 2041–20260 have been presented in Fig. 7. The changes in projected precipitation in 2041–2060 are noted as positive in the northern and south-east areas of Bangladesh, which reveals the increase in precipitation compared to the base line period. Considering these precipitation changes on a division basis, it is found that the projected precipitation has been increased greatly in the south-east regions of the Chittagong division under SSP 1.26, SSP 2.45, and SSP 5.85. The precipitation is found to have increased by 600 to 1600 mm. While the projected precipitation in the Rangpur and Sylhet divisions has moderately increased, under all SSPs except SSP 3.70, with a magnitude of 200–600 mm. A very large portion of Bangladesh, such as the entire Rajshahi, Dhaka, Khulna division, substantial parts of Chittagong, Sylhet, and Rangpur, under all SSPs, will have received slightly more precipitation than the base line period precipitation that could be ranged between 0 to 200 mm. However, the projected precipitation decreased alarmingly in the Dhaka division under all SSPs, and in the Khulna division only SSP 3.70 was found to have decreased precipitation by 0-400 mm, with the Dhaka division experiencing the greatest precipitation decrease under SSP 3.70.
3.2.2 Projected changes in annual average projected maximum and minimum precipitation in 2041–2060
In Dhaka, Rajshahi, Chittagong, Sylhet, and Rangpur, it is seen (Fig. 8) that the predicted change in maximum precipitation is found positive for all SSPs, indicating a rise in precipitation relative to the baseline precipitation. Precipitation variations are indicated as favorable in the case of Barisal for all SSPs except SSP3.70. In the Khulna division, the average annual maximum precipitation is shown to be negative. During this projected period, Chittagong has a height increase in maximum precipitation of 1670 mm under SSP1.26, whereas Khulna experiences a height drop in maximum precipitation of 611 mm with SSP3.70.
Only in Barisal and Sylhet under all SSPs is the expected change in annual average minimum precipitation determined to be positive and negative across all divisions. The following five divisions simultaneously record the positive and negative changes in precipitation. Khulna and Chittagong have seen the most beneficial developments out of all of them. However, in SSP1.26, Barisal receives the height-positive changes in minimum precipitation at 301 mm, whereas Sylhet receives the height-negative changes at 143 mm (Fig. 9).
3.2.3 Projected changes in annual average precipitation in 2061–2080
The changes in average annual precipitation throughout Bangladesh between the baseline period and the timeframe 2061–2080 have been shown in Fig. 10 under four shared socioeconomic paths (SSPs). In the northern and south-east regions of Bangladesh, which had an increase in precipitation relative to the base line era, the changes in forecast precipitation in 2061–2080 are identified as favorable. The expected precipitation has been significantly enhanced in the south-east portions of the Chittagong and Sylhet divisions under SSP 5.85 when these precipitation adjustments are taken into account on a divisional basis. There has been an increase in precipitation of 400 to 2000 mm. With the exception of SSP 2.45 for the Khulna division, the forecast precipitation has moderately risen in the Rangpur, Khulna, and Barisal divisions with a magnitude of 200–1000 mm under all SSPs. The whole Rangpur, Rajshahi, Khulna, and Barisal divisions, under SSP 1.26, SSP 3.70, and SSP 5.85, as well as significant portions of Dhaka, under SSP 5.85, will have gotten a little bit more precipitation than the base line period precipitation, which may have varied from 200 to 800 mm. However, the projected precipitation slightly decreased in the Dhaka division under all SSPs; SSP 1.26, SSP 2.45, SSP 3.70, Rajshahi and Khulna divisions only SSP 2.45 were found to have decreased precipitation by 0-400 mm, while the highest precipitation decrease was noticed in the Dhaka division under SSP 2.45.
3.2.2 Projected changes in annual average projected maximum and minimum precipitation in 2061–2080
In all divisions except Khulna, it is seen in Fig. 11 that the predicted change in maximum precipitation is found to be positive under all SSPs, indicating an increase in precipitation above the baseline precipitation. In contrast, the average annual maximum precipitation in Khulna division is determined to be negative. Chittagong has the highest increase in maximum precipitation over this projected period (1856 mm), followed by Sylhet (1671 mm), and Rangpur (1348 mm) under the same SSP5.85. However, Khulna, Bangladesh, receives the most precipitation—343 mm—under SSP2.45.
Barisal is the only division to show positive annual average minimum precipitation changes under all SSPs throughout this forecast period. As a result, precipitation changes in the following divisions are both negative and positive. The following five divisions, with the exception of Sylhet, may generally be described as positive. That alludes to improvements made as a result of most SSPs. However, with SSP5.85, the lowest precipitation height positive changes are reached at 451 mm in Barisal, followed by 414 mm in Chittagong. On the other side, Sylhet under SSP3.70 obtains the height negative changes in minimum precipitation at 211 mm (Fig. 12).
3.2.4 Projected changes in annual average precipitation in 2081–2100
Figure 13 shows the variations in average yearly precipitation throughout Bangladesh between the baseline period and the term 2081–2100 for four shared socioeconomic paths (SSPs). The northern and south-east regions of Bangladesh are identified as having positive changes in anticipated precipitation for the years 2081–2100, which indicates an increase in precipitation over the baseline period. When these variations in precipitation are taken into account on a divisional basis, it is seen that under SSP 3.70 and SSP 5.85, the expected precipitation has been considerably enhanced in the northern portions of the Rangpur and Sylhet divisions. It has been determined that the precipitation has risen by 1100 to 1900 mm. Almost all SSPs 1.26, SSP 2.45, SSP 3.70, and SSP 5.85 have an imagined range of (300–900) mm, even if the predicted precipitation in the Sylhet division has somewhat risen, especially under SSP 1.26, SSP 2.45, and Rangpur division. All SSPs have a magnitude of 200–1000 mm, with the exception of SSP 1.26 in the Khulna and Rajshahi divisions and SSP 5.85 in the Dhaka division. Under all SSPs, the anticipated precipitation did, however, marginally drop in the Dhaka division. The Dhaka division under SSP 1.26, followed by 2.45, was found to have decreased precipitation by 0-400 mm, whereas the division under SSP 1.26, followed by 2.45, saw the largest fall in precipitation.
3.2.2 Projected changes in annual average projected maximum and minimum precipitation in 2041–2060
It is observed (Fig. 9) that the projected change in maximum precipitations are found positive in Chittagong, Rajshahi, Barisal, Rangpur and Sylhet under all SSPs, that reveals the increase in precipitation compare to the baseline precipitation. But the average annual maximum precipitation is found to be negative in Khulna division under all SSPs; the same is in Dhaka except the SSP1.26. In the final segment of the projection period, 2080–2100, the maximum increase in maximum precipitation of 1984 mm is obtained in Sylhet and followed by 1707 mm in Rangpur under the SSP5.85. Here, a height decrease in maximum precipitation of 484 mm is obtained in Dhaka under SSP1.26.
In the last segment of the projection period, 2080–2100, four divisions, namely Dhaka, Khulna, Chittagong, and Barisal, are obtained to be positive in the case of annual average minimum precipitation changes under all SSPs. Hence, the remaining three divisions are experiencing both negative and positive changes in annual average minimum precipitation. Except Sylhet, the other two divisions can be characterized as positive most of the time. That refers to positive changes under most SSPs. However, the height positive changes in minimum precipitation are obtained at 516 mm in Barisal and followed by 349 mm in Chittagong under SSP5.85. On the other hand, the height negative changes in minimum precipitation are obtained at 148 mm in Sylhet under SSP1.26 (Fig. 15).