## 3 Results
### The Effects of ET Variations on Estimation of Runoff and Water Storage Changes  
2.1 The Water Balance in the Murrumbidgee River Catchment (MRC) Using Australian Water Availability Project (AWAP) Datasets  
Figure 4 shows the annual and monthly water balance in the MRC using AWAP datasets. The mean annual precipitation, ET, runoff, and water storage changes are 518.0 mm, 464.1 mm, 49.5 mm, and 4.4 mm, respectively. The years of 2002, 2006, and 2009 were the dry years, while 2010, 2011, and 2016 were wet years. In most years, the precipitation is largely lost by ET, and in some years even the latter is larger than the former due to relatively less precipitation and consumption of the soil water. The runoff is low except in the very wet years, and the water storage is in a deficit condition. This situation was most serious in 2006.  
The precipitation and ET in the MRC are concentrated in the period from December to February. The runoff only appeared in heavy rain years, for example, in 2010, 2011, and 2016. In some months, ET is more than precipitation, which leads to water storage changes: a recharge in heavy rain years and a deficit in drought years.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & **A\_ET** & **C\_ET** & **G\_ET** & **M\_ET** & **T\_ET** & **A\_ET** & **C\_ET** & **G\_ET** & **M\_ET** & **T\_ET** \\ \hline  & & & **Yearly** & & & & & **Monthly** & & \\ \hline Mean (mm) & 464.14 & 473.53 & 529.91 & 352.32 & 450.37 & 38.68 & 39.46 & 44.16 & 29.36 & 37.53 \\ N & 16 & 12 & 16 & 16 & 16 & 192 & 144 & 192 & 192 & 192 \\ NSE h & 1 & 0.84 & 0.07 & \(-\)1.42 & 0.61 & 1 & 0.74 & 0.61 & 0.21 & 0.34 \\ \(R^{2}\) & 1 & 0.87 & 0.93 & 0.82 & 0.87 & 1 & 0.77 & 0.82 & 0.49 & 0.52 \\ RMSE h (mm) & 0 & 33.45 & 71.90 & 116.25 & 46.43 & 0 & 9.31 & 11.21 & 15.84 & 14.50 \\ RSR j & 0 & 0.40 & 0.96 & 1.56 & 0.62 & 0 & 0.51 & 0.63 & 0.89 & 0.81 \\ PBIAS k & 0 & 0.03 & 0.14 & \(-\)0.24 & \(-\)0.03 & 0 & 0.03 & 0.14 & \(-\)0.24 & \(-\)0.03 \\ MAE l (mm) & 0 & 27.20 & 65.82 & 11.78 & 38.23 & 0 & 7.15 & 7.91 & 11.33 & 11.65 \\ \hline \hline \end{tabular} Note: h Nash–Sutcliffe efficiency (NSE), i root mean square error (RMSE), j root mean square error observation standard deviation ratio (RSR), k percent bias (PBIAS), and l mean absolute error (MAE).  
\end{table}
Table 2: Comparison of the four evapotranspiration (ET) products with the AWAP ET.  
3.2.2. The Effects of ET Variations on Runoff Estimation  
Figure 5 shows the annual runoff estimated using the four ET products combining the AWAP precipitation and water storage data. Compared with the AWAP runoff, the runoff estimated using the MODIS ET is much larger, while the runoff estimated using the TerraClimate ET is larger in some years and less in other years and even is negative in 2010. The runoff estimated using the GLDAS ET is much less than the AWAP runoff and even becomes negative. The runoff estimated using the CSIRO ET is complex, because it is larger or less than the AWAP runoff in some years but is negative in other years. The mean annual runoff estimated using the ET products from AWAP, CSIRO, GLDAS, MODIS, and TerraClimate are 49.5 mm, 34.4 mm, -16.3 mm, 161.3 mm, and 63.2 mm respectively. Application of the CRISO and GLADS ET products results in the underestimation of runoff, on the contrary, the MODIS and TerraClimate ET products result in the overestimation of runoff. The runoff estimated using the GLDAS ET is negative, while the runoff estimated using the MODIS ET is more than triple that of the AWAP runoff.  
Figure 4: The annual (**a**) and monthly (**b**) water balance in MRC.