Temporal and spatial aggregation of rainfall extremes over India under anthropogenic warming

Abstract

India experienced several unprecedented floods in the recent decades. The increase in the extreme rainfall events (EREs) is the primary cause for these floods, manifesting its societal impacts. The daily downscaled and bias corrected (DBC) Coupled Model Intercomparison Project Phase 6 (CMIP6) rainfall and sea surface temperature (SST) are prepared for the Indian region and are utilized to examine the characteristics of EREs. The DBC products capture the characteristic features of EREs for the baseline period, which inspired us to assess the EREs over India in CMIP6 future projections. Consistent with the observations, DBC product shows ~ 8% of Indian land found to experienced extremely heavy rainfall associated with the long duration EREs in the baseline period. However, area and extreme rainfall thresholds are projected to increase by about 18(13)% and 58(50)%, respectively in the far future under SSP5-8.5 (SSP2-4.5) emission scenario relative to the baseline period. A two-fold-65(62)% increase in long-duration EREs compared to the short-duration EREs and substantial warming ~ 2.4(2.9) ^oC of Indian Ocean SSTs in the far future under SSP5-8.5 (SSP2-4.5) emission scenario compared to baseline period are reported. These findings may provide fundamental insights to formulate national climate change adaptation policies for the EREs.

Figure 1

Multi model mean of Indian summer monsoon (JJAS) R95 thresholds (mm/day) over India for the historical, SSP2-4.5 (SSP245), and SSP5-8.5 (SSP585) scenarios varying from baseline (a), observations (IMD) (b), near-future (c), and far-future (d). Before DBC (MMM) and after DBC (MMM-bc). Values in blue (red) color represents the pattern correlation (RMSE). Values in black color represents the mean thresholds rainfall (mm/day). (Figure created using the Matlab R2023a; https://in.mathworks.com/).

Figure 2

Composite of precipitation anomalies for the base-line period during long duration and short duration of EREs over India in observations (IMD) before DBC (MMM), and after DBC (MMM-bc). Values in blue (red) color represents the pattern correlation (RMSE). Improvement of mean rainfall after DBC is shown in %. Insignificant (< 95% confidence level) regions are masked with “ + ”. (Figure created using the Matlab R2023a; https://in.mathworks.com/).

Figure 3

Composite of SST anomalies for the base-line period corresponds to long duration and short duration of EREs over India, for observations (NOAA), before DBC (MMM), and after DBC (MMM-bc). Values in blue (white) color represents the pattern correlation (RMSE). Significant (> 95% confidence level) regions are masked with “.”. (Figure created using the Matlab R2023a; https://in.mathworks.com/).

Figure 4

Composite of precipitation anomalies (w.r.to baseline period climatology) during long duration and short duration of EREs for SSP2-4.5 (SSP245), and SSP5-8.5 (SSP585) scenarios during near future and far future periods. Values in black color represents the mean rainfall anomalies averaged over India. Improvement of mean rainfall after DBC is shown in %. Insignificant (< 95% confidence level) regions are masked with “ + ”. (Figure created using the Matlab R2023a; https://in.mathworks.com/).

Figure 5

Composite of SST anomalies (w.r.to baseline period climatology) during long duration and short duration of EREs for SSP2-4.5 (SSP245), and SSP5-8.5 (SSP585) scenarios during near future and far future periods. Values in white color represents the mean SST anomalies averaged over the Indian Ocean. Significant (> 95% confidence level) regions are masked with “.”. (Figure created using the Matlab R2023a; https://in.mathworks.com/).

Figure 6

(a) Number of short and long duration EREs over monsoon core region during JJAS season (bars) and associated mean rainfall over India (line) for high emission scenario (SSP5-8.5) of MMM-bc product. The equation in red and blue color represents the trend of short and long duration of EREs for the period 2020–2100, respectively. (b) Area (%) experiencing the twofold of rainfall exceeding the mean rainfall over India associated with the EREs for the base period. (c) duration of ERES over monsoon core region. (d) All India mean rainfall associated with the EREs over monsoon core region. (Figure created using the Matlab R2023a; https://in.mathworks.com/).