# Controlled Drainage Effectiveness in Reducing Nutrient Outflow in Light of Climate Changes
## 4 Discussion  
Based on the results, the analysis of withholding outflow on the drainage network for the SSP370 pathway in the near future indicates that the efficiency of using CD solutions will increase compared to the present state. Withholding outflow on 1 March allows GWT to increase by an average of 35, 23, and 21 cm for the GFDL climate change model, by 31, 28, and 25 cm for MPI, and by 24, 25, and 19 cm for UKESM in wet, normal, and dry years, respectively, compared to FD. Comparing the present climate conditions [34] to the near future, we have also considered the possibility of using the proposed methodology to estimate the efficiency of using CD solutions. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{\
\begin{tabular}{c} **Drainage** \\ **Variants** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Initial GWT** \\ **(cm b.s.L)** \\ \end{tabular} } & \multicolumn{6}{c}{**Reduction in NO\({}_{\text{3}}\)–N and PO\({}_{\text{4}}\) (\%)**} \\ \cline{3-8}  & & & **Wet** & & **Normal** & **Dry** \\ \hline \multicolumn{8}{c}{GFDL} \\ \hline \multirow{8}{*}{CD} & & 40 & 98.51 & g & 98.09 & h & 98.00 & f \\  & 1.03 & 60 & 98.40 & g & 98.06 & h & 97.94 & f \\  & 80 & 98.23 & g & 97.58 & h & 97.49 & f \\ \cline{2-8}  & & 40 & 22.39 & c, d, e & 14.85 & a, b, c, d, e & 11.42 & a, b, c, d \\  & 15.03 & 60 & 27.51 & d, e & 18.85 & c, d, e & 14.73 & a, b, c, d \\  & 80 & 36.86 & e, f & 28.62 & d, e, f & 23.53 & d, e \\ \cline{2-8}  & & 40 & 1.78 & a, b & 3.06 & a, b, c & 0.31 & a \\  & 1.04 & 60 & 2.25 & a, b & 4.04 & a, b, c & 0.36 & a \\  & 80 & 3.15 & a, b & 6.39 & a, b, c & 0.64 & a, b \\ \cline{2-8}  & & 40 & 0.75 & a & 0.00 & a & 0.00 & a \\  & 15.04 & 60 & 0.92 & a & 0.00 & a & 0.00 & a \\  & 80 & 1.20 & a & 0.00 & a & 0.00 & a \\ \hline \multicolumn{8}{c}{MPI} \\ \hline \multirow{8}{*}{CD} & & 40 & 98.37 & g & 98.32 & h & 98.15 & f \\  & 1.03 & 60 & 98.23 & g & 98.35 & h & 98.06 & f \\  & 80 & 98.19 & g & 98.26 & h & 97.76 & f \\ \cline{2-8}  & & 40 & 85.02 & g & 91.97 & h & 94.14 & f \\  & 15.03 & 60 & 92.09 & g & 95.67 & h & 95.89 & f \\  & 80 & 95.99 & g & 97.45 & h & 96.33 & f \\ \cline{2-8}  & & 40 & 1.41 & a & 1.05 & a, b & 5.32 & a, b \\  & 1.04 & 60 & 1.72 & a, b & 1.30 & a, b & 7.18 & a, b, c, d \\  & 80 & 2.25 & a, b & 1.76 & a, b & 12.48 & a, b, c, d \\ \cline{2-8}  & & 40 & 0.00 & a & 0.00 & a & 0.02 & a \\  & 15.04 & 60 & 0.00 & a & 0.00 & a & 0.03 & a \\  & 80 & 0.00 & a & 0.00 & a & 0.04 & a \\ \hline \multicolumn{8}{c}{UKESM} \\ \hline \multirow{8}{*}{CD} & & 40 & 98.09 & g & 98.31 & h & 98.10 & f \\  & 60 & 98.21 & g & 98.33 & h & 98.12 & f \\  & 80 & 98.14 & g & 98.24 & h & 97.92 & f \\ \cline{2-8}  & & 40 & 22.96 & c, d, e & 29.51 & e, f & 17.42 & b, c, d \\  & 15.03 & 60 & 29.22 & d, e, f & 37.27 & f & 22.80 & c, d, e \\  & 80 & 43.92 & f & 55.25 & g & 35.73 & e \\ \cline{2-8}  & & 40 & 9.96 & a, b, c & 12.48 & a, b, c, d & 6.13 & a, b, c \\  & 1.04 & 60 & 13.26 & a, b, c, d & 16.80 & b, c, d, e & 8.62 & a, b, c, d \\  & 80 & 22.48 & c, d, e & 28.84 & d, e, f & 15.67 & a, b, c, d \\ \cline{2-8}  & & 40 & 7.22 & a, b, c & 7.98 & a, b, c & 5.73 & a, b \\  & 15.04 & 60 & 9.87 & a, b, c & 10.98 & a, b, c & 8.10 & a, b, c, d \\  & 80 & 17.97 & b, c, d & 19.34 & c, d, e & 14.94 & a, b, c, d \\ \hline \hline \end{tabular} Notes: Different letters (a to f) indicate significant differences (\(p\leq 0.05\)) between variants for each group of years according to [PERSON]’s test.  
\end{table} 
Table 8: NO\({}_{\text{3}}\)–N and PO\({}_{\text{4}}\) reduction for different variants of CD practice in wet, normal, and dry years for GFDL, MPI, and UKESM models. future using CD on 1 March, the highest increase in GWT was achieved for the GFDL and MPI models for wet years of 4 to 8% and 3 to 6%, respectively, and for initial depths of 40 and 80 cm b.s.l. Similarly, the highest increases in GWT were recorded for the MPI model on 15 March for wet, normal, and dry years, ranging from 10-19%, 7-18%, and 2-15%, respectively.