Hydro-climatic shifts of worldwide river basins in the past century

Understanding of river basins hydro-climatic shifts and their drivers in the past is of significant importance for the prediction of future projections. This study evaluates the hydro-climatic shifts of worldwide river basins through Budyko Framework at 20 years’ time steps from 1901 to 2000 based on field-measured runoff data. It is also aimed to identify whether shifts are related to climate change, human interventions, or both. The selected river basins cover a wide range of climates and topography. The movement of basins in the Budyko Space is quantified from the first twenty years to the next twenty years. It is found that 47% of the catchments observed an increase in their aridity and evaporative indices between a period of comparison from 1901 to 1920 and 1921 to 1940. An increase in both indices means that these catchments have moved toward a drier state and more precipitation is partitioned into evaporation as compared to runoff. However, it is observed that during periods from 1961 to 1980 & 1981 to 2000 this percentage has reduced to 20% only and more number of catchments (47%) have observed a decrease in the aridity index as well as the evaporative index. It is seen that major hydro-climatic shifts of river basins have occurred from an increase in aridity and evaporative indices to a decrease in both indices from start to the end of the past century. It is concluded that with time, more number of catchments have moved towards a wet state and observed an increase in runoff as compared to the past. Although, more catchments observed a shift but the magnitude of movement is not that much high for all of them. It is observed that the catchments with a high aridity and evaporative index are more sensitive to change. On average for all time periods of comparison, it is found that for 90% of the catchments the climate change is the main driver of hydro-climatic shifts and the change for the remaining is caused by combined effects of climate and human interventions. This understanding of hydroclimatic shifts of river basins over time can be helpful for water management practices, especially for the catchments which are sensitive to change and also have observed an increase in runoff.