GRACE AND GRACE-FO UNRAVEL THE IMPACTS OF TROPICAL CYCLONES ON ARABIA’S HYDROLOGY: NAJD WATERSHED AS A CASE STUDY

Global warming has led to a significant increase in the frequency of intense tropical storms both worldwide and in the Arabian basin. Within the last three decades, Arabia has experienced 12 cyclones, with three classified as extremely severe cyclonic storms (ESCS) and one as a super cyclonic storm. These storms brought significant amounts of rainfall inland, potentially contributing to the recharge of groundwater in the hyper-arid regions of southern Arabia where data on water resources is limited. In order to assess the potential impacts of TC precipitation (TCP) events on total water storage (TWS), this study was conducted using the Najd watershed (200,000 km²) as a test site. The following scheme is employed; 1) identify TCP events and estimate the contribution of TCP to the total precipitation, 2) estimate the change in TWS over the watershed from GRACE, GRACE-FO missions, and GLDAS land surface model, during the operational period (2002–2021), 3) develop a 2D surface water model that estimates TCP partitioning in the region, 4) calibrate the model using temporal variations of inundated areas extracted from (Sentinel-1, 2), following the TCP event. Preliminary findings show that GRACE_TWS time series exhibit a direct response to TCP regardless of TCP's short occurrence time, followed by a sharp decline, possibly due to high evaporation rates. However the system recovered by (3 km³) following two cyclone landfalls in 2018, depletion continued with a decreasing trend of -0.16 km³. We believe that the low residence time of water is attributed to the limited area of the deep aquifer (Umm-Er-Radhuma) outcrops where recharge takes place.