Figure 6
TWSA trends in the EIB and its 16 closed basins were analyzed using the average series from the five GRACE products. Figure 7 presents the annual and monthly TWSA trends for different basins for 2002–2020. As opposed to the large variation in precipitation trends each month, there was only a slight variation in the TWSA trends between each month. The standard deviation of the magnitude of TWSA trends ranged between 0.3 and 0.9 among the different closed basins, while it was 0.4 for the entire EIB. This is because the seasonal variation of soil moisture, glacier/snow, surface and ground waters in TWS is much lower than precipitation. The lowest seasonal variation occurred in the QPB, as there are a large number of solid water bodies (glacial and snow covered) in this region, and these water bodies were relatively stable in terms of TWS. There were significant decreasing trends in the annual and monthly TWSA in the EIB, exceeding a significance level of p < 0.01.
At the closed basin scale, although the annual TWSA was decreasing in most basins, there were slight and significant increasing trends in the QPB and QB, with the magnitude of 0.2 and 5.7 cm/10a, respectively. The increasing annual and monthly TWSA in the QB exceeded the significance level of p < 0.001. The annual and monthly TWSA in the BLB showed non-significant decreasing trends. There were significant decreasing trends in annual TWSA in the remaining 12 basins. With the exception of the MPLB and MPIRB, the significance levels in the other ten basins exceeded p < 0.01. The decreasing magnitude was highest in the IIRB and CSB, at -9.2 and -8.9 cm/10a, respectively.