Figure 7
Across the entire EIB, it was expected that the increase in
precipitation would cause an increase in the TWSA; however, the TWSA
showed a significant decreasing trend. This indicates that the increase
in water consumption by the AET was the main factor driving the
significant decrease in the TWSA. Figure 8 shows the trends in the
annual precipitation, AET and TWSA, mean annual precipitation and AET,
and the accumulated (P – ET) values in each closed basin. In general,
precipitation, AET, and changes in TWSA were in balance at the closed
basin scale; however, the changes in P, AET and TWSA were not in
balance. As such, the contribution from changes in precipitation and AET
to changes in TWSA at the closed basin scale was qualitatively analyzed.
Similar to the EIB, there were significant decreasing trends in the TWSA
when precipitation exhibited increasing trends in most basins, including
the ASB, GHCB, HRB, IMPB, ISB, MPLB, MPIRB, TaRB, and TB. This indicates
that the increase in AET was the main cause of the significant decrease
in the TWSA in these basins. In the CSB and JB, the decrease in
precipitation and the increase in AET led to a decrease in the TWSA. The
increasing magnitude of AET was three and 1.5 times the decreasing
magnitude of precipitation in the CSB and JB, respectively. This
indicates that the increase in AET contributed to the decrease in the
TWSA to a greater extent than did the decrease in precipitation. The
results for the BLB, IIRB, and TuRB were the opposite to those of the
aforementioned basins. It was expected that the decreasing AET would
induce an increase in the TWSA; however, the TWSA exhibited significant
or non-significant decreasing trends in these basins. This indicates
that the decrease in precipitation was the main factor affecting the
decrease in the TWSA of these basins. The decreasing precipitation in
the QPB may cause a decrease in the TWSA; however, there was a slightly
increasing trend in the TWSA of the basin, largely due to the decrease
in the AET. The increasing in the AET for the QB may cause a decrease in
TWSA; however, there was a significant increasing TWSA in the basin
largely caused by the increasing precipitation.
According to the physical influence mechanism, the change in the TWSA in
a closed basin is directly correlated to the accumulated (P – ET), and
this study was able to verify this. For the depth results, the
accumulated (P – ET) for 2002–2020 was -5.3 cm/10a; this is consistent
with the decreasing magnitude of TWSA in the EIB. At the basin scale,
the magnitude of trends of TWSA in each basin ranged from -9.2 to 5.7
cm/10a, with an average of -3.0 cm/10a. The accumulated (P – ET) in
each basin varied from -9.6 to 6.2 cm/10a, with a mean of -3.1 cm/10a.
There was a high consistency between the TWSA changes and accumulated (P
– ET). The results were similar to the depth results for the EIB and
each basin. The TWSA decreased by -5615.6×108m3/10a during 2002–2020 in the EIB. This annual
reduction in the TWSA in the EIB was approximately equivalent to the
mean annual runoff of the Yellow River. At the basin scale, the
decreasing magnitude of the TWSA was relatively higher in the western
and southwestern basins of the EIB, including the CSB, IIRB, ASB, and
HRB; the magnitude of the decrease in the CSB exceeded than
-3300×108 m3/10a. The amount of
accumulated (P – ET) was consistent changes in the TWSA; the
R2 between the two series composed from each basin
value reached 0.99.