Effect of watershed disturbance on seasonal hydrological drought: An improved double mass curve (IDMC) technique

The goal of the current study is to examine the relative role of watershed disturbance on the seasonal hydrological drought. We propose a new methodology that combines the two-parameter Budyko equation and improved double mass curve (IDMC) technique to remove the effect of climate change from the total change in the seasonal hydrological drought. In particular, we analyze the relative role of watershed disturbance and forest change in the changes of seasonal hydrological drought using Yaak River watershed in Montana, U.S. as an example. The hydrological drought is defined based on the threshold level approach. In addition, the sensitivity of hydrological drought to the changes of forest condition is performed based on the basin average normalized difference vegetation index (NDVI). The proposed method can be applied to quantify the effect of watershed disturbance on the seasonal drought. Seasonal flow shows the different nature of response to the watershed disturbance. Spring flow decrease is primarily due to the watershed disturbance. On the other hand, watershed disturbance offsets climate change effect on summer flows. The changes in hydrological drought due to watershed disturbance decrease (increase) with the threshold during spring (summer). The contribution of forest disturbance to the change in drought due to watershed disturbance during the summer is as large as 75%. The study has a promising potential in hydrological studies because watershed characteristics play a crucial role in terrestrial water storage, evapotranspiration, and discharge.