Characterization of interannual and seasonal variability of hydro-climatic trends in the Upper Indus Basin

High-resolution seasonal and annual precipitation climatologies for the Upper Indus Basin were developed on the basis of 1995-2017 precipitation normals obtained from four-gridded datasets (APHRODITE, CHIRPS, PERSIANN-CDR, and ERA5) and the quality-controlled high- and mid-elevation station observations. Monthly precipitation is estimated through the anomaly method at the catchment scale, and then, it is compared with the observed discharges over the 1975-2017 period for verification and detection of changes in the hydrological cycle. Running trends and spectral analysis on the precipitation gridded dataset were performed. The Mann-Kendall test was employed to detect the significance of trends whereas the Pettitt test was used to identify change points in precipitation and discharge time series. The results indicate that the bias corrected CHIRPS precipitation, followed by the ERA5, performed better in terms of RMSE, MAE, MAPE, and BIAS against the rain gauge observations. The running trend analysis exhibits a slight increase in annual precipitation, but it shows significant increase in winter precipitation. A runoff coefficient greater than one, especially in the glacierized sub-catchments of Shigar, Shyok, Astore, and Gilgit, indicates that precipitation is likely to be underestimated and glacial melt provides excess runoff volumes in a warming climate. Streamflow variability is found to be pronounced at the seasonal rather than at the annual scale. The annual discharges at Shyok, Gilgit, and Indus at Kachura gauges are slightly significantly increasing. Seasonal discharge analysis reveals more complex regimes, varying in different catchments, and its comparison with precipitation variability favors a deeper understanding of precipitation, snow-, and ice-melt runoff dynamics, addressing the hydroclimatic behavior of the Karakoram region and some weaknesses in the monitoring network at high altitude.