## 4 Results and Discussion
### Variation Characteristics of Honghu Lake
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline
**Year** & **Area/Year** & **January** & **February** & **March** & **April** & **May** & **June** & **July** & **August** & **September** & **October** & **November**December** \\ \hline \multirow{2}{*}{Maximum} & Area & 293.75 & 298.53 & 298.90 & 280.99 & 295.97 & 283.37 & 294.89 & 282.47 & 303.26 & 294.23 & 295.12 & 296.06 \\  & Year & 2004 & 2000 & 2005 & 2010 & 2003 & 2000 & 2003 & 2010 & 1996 & 2010 & 2003 & 1996 \\ \hline \multirow{2}{*}{Minimum} & Area & 258.65 & 218.89 & 230.04 & 140.20 & 153.49 & 232.43 & 243.04 & 237.27 & 208.69 & 198.02 & 236.25 & 242.07 \\  & Year & 2013 & 1989 & 2006 & 2011 & 2011 & 2010 & 2012 & 2001 & 2001 & 2001 & 2001 \\ \hline \multicolumn{2}{c}{Max/Min ratio} & 1.14 & 1.36 & 1.30 & 2.00 & 1.93 & 1.22 & 1.21 & 1.19 & 1.45 & 1.49 & 1.25 & 1.22 \\ \hline \end{tabular}
\end{table} 
Table 1: Inter-Annual variability of area of the Honghu Lake (km\({}^{2}\)) by month from the 1990s to 2013. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline
**Year** & **Area/Year** & **1990’s** & **2000** & **2001** & **2002** & **2003** & **2004** & **2005** & **2006** \\ \hline \multirow{2}{*}{Maximum} & Area & 303.3 & 298.5 & 284.6 & 290.0 & 296.0 & 293.8 & 298.9 & 266.1 \\  & Month & September & February & January & December & May & January & March & January \\ \hline \multirow{2}{*}{Minimum} & Area & 218.9 & 261.1 & 198.0 & 243.7 & 277.4 & 217.3 & 229.6 & 200.1 \\  & Month & February & August & October & March & April & April & May & April \\ \hline \multicolumn{2}{c}{Max/Min ratio} & 1.39 & 1.14 & 1.44 & 1.19 & 1.07 & 1.35 & 1.30 & 1.33 \\ \hline \multicolumn{2}{c}{**Year**} & **Area/Year** & **2007** & **2008** & **2009** & **2010** & **2011** & **2012** & **2013** & **1990s-2013** \\ \hline \multirow{2}{*}{Maximum} & Area & 267.7 & 277.6 & 284.7 & 294.2 & 270.4 & 278.8 & 278.2 & 303.3 \\  & Month & January & November & March & October & January & March & December & \\ \hline \multirow{2}{*}{Minimum} & Area & 233.3 & 220.9 & 241.4 & 217.0 & 140.2 & 197.7 & 210.7 & 140.2 \\  & Month & May & October & October & May & April & April & April & \\ \hline \multicolumn{2}{c}{Max/Min ratio} & 1.15 & 1.26 & 1.18 & 1.36 & 1.93 & 1.41 & 1.32 & 2.16 \\ \hline \end{tabular}
\end{table} 
Table 2: Intra-Annual variability of area of the Honghu Lake (km\({}^{2}\)) from the 1990s to 2013. The time series of the water-surface area of the lake between the 1990s and 2013 is presented in Figure 4. To study the change trend of the lake's water-surface area, we perform a linear least- square regression fit between the areas and time. A decreasing trend with significance level of \(>\)95% is detected. The water-surface area fluctuated widely from 140.2 km\({}^{2}\) to 303.26 km\({}^{2}\) in the observed period, making a decrease rate of 0.1647 km\({}^{2}\cdot\)year\({}^{-1}\). The annual mean areas between the 1990s and 2013 are further calculated. The results indicate decrease rates of 1.5632 km\({}^{2}\cdot\)year\({}^{-1}\) beginning in the 1990s and 1.813 km\({}^{2}\cdot\)year\({}^{-1}\) beginning in 2000. We can deduce from these results that the water-surface area in the Honghu Lake is decreasing, especially after 2000. Figure 3: Minimum and maximum area distributions of Honghu Lake each year from 1990s to 2013