21st century precipitation and monsoonal shift over Pakistan and Upper Indus Basin (UIB) using high-resolution projections.

There is research evidence that due to global warming, global precipitation and monsoon area have shown a shift which needs to be analyzed at regional scale. This study analyses future precipitation and monsoon spatial shift over Pakistan and Upper Indus Basin (UIB) based on latest Coordinated Regional Climate Downscaling Experiment - Coordinated Output for Regional Evaluations (CORDEX-CORE) high resolution projections (25 km) for the South Asian domain. Three global climate models from Coupled Model Intercomparison Project Phase 5 (CMIP5) (MIROC5, NorESM1-M and MPI-ESM-MR) provided the lateral boundary conditions for the Regional Climate Model (RegCM4) under Representative Concentration Pathways 2.6 (RCP2.6) and RCP8.5 scenarios. Results indicate that JJA precipitation over Upper Indus Basin (UIB which also includes North Pakistan) is projected to increase more under RCP8.5 and less under RCP2.6 while for Pakistan it shows slightly increase (decrease) in RCP2.6 (RCP8.5). The results also show a projected expansion in monsoon area in UIB and northward shift of MCR which corresponds with future precipitation changes in the area and hence indicate the penetration of monsoon system over UIB under higher warming scenario. The changes in monsoon precipitation and domain are related to the changes in wind circulation patterns at 850 hPa and 200 hPa atmospheric levels.

Hydrological projections over the Upper Indus Basin at 1.5 °C and 2.0 °C temperature increase.

We analyse an ensemble of statistically downscaled Global Climate Models (GCMs) to investigate future water availability in the Upper Indus Basin (UIB) of Pakistan for the time horizons when the global and/or regional warming levels cross Paris Agreement (PA) targets. The GCMs data is obtained from the 5th Phase of Coupled Model Inter-Comparison Project under two Representative Concentration Pathways (RCP4.5 and RCP8.5). Based on the five best performing GCMs, we note that global 1.5 °C and 2.0 °C warming thresholds are projected in 2026 and 2047 under RCP4.5 and 2022 and 3036 under RCP8.5 respectively while these thresholds are reached much earlier over Pakistan i.e. 2016 and 2030 under RCP4.5 and 2012 and 2025 under RCP8.5 respectively. Interestingly, the GCMs with the earliest emergence at the global scale are not necessarily the ones with the earliest emergence over Pakistan, highlighting spatial non-linearity in GCMs response. The emergence of 2.0 °C warming at global scale across 5 GCMs ranges from 2031 (CCSM4) to 2049 (NorESM) under RCP8.5. Precipitation generally exhibits a progressive increasing trend with stronger changes at higher warming or radiative forcing levels. Hydrological simulations representing the historical, 1.5 °C and 2.0 °C global and region warming time horizons indicate a robust but seasonally varying increase in the inflows. The highest inflows in the baseline and future are witnessed in July. However, the highest future increase in inflows is projected in October under RCP4.5 (37.99% and 65.11% at 1.5 °C and 2.0 °C) and in April under RCP8.5 (37% and 62.05% at 1.5 °C and 2.0 °C). These hydrological changes are driven by increases in the snow and glacial melt contribution, which are more pronounced at 2.0 °C warming level. These findings should help for effective water management in Pakistan over the coming decades.