Propagation and spatial distribution of drought in a groundwater catchment

Natural droughts are usually caused by a period of lower than average precipitation. The resulting shortage in precipitation propagates through the hydrological system causing drought in the different segments of the hydrological system (unsaturated zone, saturated groundwater, surface water). To analyse the propagation and spatial distribution of the drought in the groundwater system, drought is analysed simultaneously in simulated recharge, hydraulic heads and groundwater discharge for a groundwater catchment (Pang, UK). The recharge and hydraulic heads are simulated and analysed spatially. The groundwater discharge is analysed in four reaches along the stream. Comparison of droughts in the recharge and heads shows that the droughts are greatly attenuated and delayed in the groundwater system. Comparison of the droughts in the heads and the discharge shows the opposite effect, so that the droughts in the discharge resemble more the droughts in the recharge than those in the hydraulic heads. The faster response in the groundwater discharge compared to the hydraulic heads is probably caused by the non-linear relationship between groundwater storage and discharge. Thus in the recharge and in the discharge, there are many short droughts, whereas in the hydraulic head fewer, more severe droughts occur. It is likely that these results hold not only for the Pang catchment but also generally for catchments with a large groundwater system and a non-linear groundwater discharge relationship. The spatial distribution of the droughts in the hydraulic heads shows that short droughts are more severe near the streams, as they are attenuated further away. Long periods of below average recharge have relatively more effect near the groundwater divide. The spatial distribution of the droughts in the groundwater discharge is such that upstream the droughts are more attenuated than downstream.