## 4 Results and Discussion
### Influence Factors
#### 4.2.2 Human Activities  
In the present study, human activities are characterized by land use change. Land use data show that the main types of agricultural land in the area under study are dryland, paddy and pond, by 2010, which accounted for 30.31%, 28.95% and 22.39% of the total land area, respectively. Therefore, the outflow of the Honghu Lake is calculated by using the following simplified formula. \[Q_{out}\equiv A_{1}(\mathrm{w}_{1}-P)+A_{2}(\mathrm{w}_{2}-P)+A_{3}(\mathrm{w} _{3}-P) \tag{8}\]  
where \(\mathrm{w}_{1}\), \(\mathrm{w}_{2}\) and \(\mathrm{w}_{3}\) are the water consumption for drought crops, paddy rice and aquaculture, respectively; and \(A_{1}\), \(A_{2}\) and \(A_{3}\) are the areas of drought crops, paddy rice, and aquaculture, respectively. Field investigation carried out by the task team indicates that two kinds of drought crops, namely, corn and cotton, are mainly grown in this area. The water consumption of corn is 401.2 mm throughout the growing season, and its daily water consumptions are 2.61, 6.29, 5.36 and 4.66 mm at the seedling, jointing, heading and filling stages, respectively [40]. The water consumption of cotton is 473.4 mm throughout the growing season, and its daily water consumptions are 1.54, 3.79, 4.55 and 1.18 mm at the seedling, bud, flowering and boll-opening stages, respectively [41]. Double-cropping rice is normally transplanted into the fields from the end of April to early May. The water consumption for soaking this crop is 129 mm before transplanting. After transplanting, the total water consumption is approximately 652.6 mm, 150 mm of which is for growth in the first 30 days. After the growing stage, the daily water consumptions are 4.1, 4.2, 6.5, 5.8, 5.1 and 2.9 mm at the greenup, tillering, booting, heading, milk-ripe and maturity stages, respectively [42]. Ponds are injected with 500 mm of water to raise water levels before stocking with fish for aquaculture. The daily water consumption for evaporation and infiltration in aquaculture ranges from 5 to 7 mm [43]. Thus, aquaculture consumes greater amounts of water than rice, and the water requirements of rice are much larger than those of drought crops. In the calculation process, we assume that all drought crops in the area are cotton. From 1990 to 2010, the paddy areas in Honghu city and Jianli county significantly decreased by 339.29 km\({}^{2}\) accounting for 6.02% of the two counties' area, whereas the pond area significantly increased by 369.76 km\({}^{2}\) accounting for 6.56%. Considering the period covered by the land use data over three phases, we select the representative wet and dry years, as shown Figure 6. Using Equation (8), we then calculate the water requirement for agricultural irrigation and aquaculture in Honghu City and Jianli County during these years. The annual precipitations in the wet and dry years range from 1335.9 to 1523.5 and 940.6 to 1096.1 mm, respectively. Figure 6 illustrates the water demand for the three types of land use in the April-May and June-October periods. Significant characteristics of water demand for agriculture can be observed; under similar agricultural structures, the water demand for agriculture in the dry years is much higher than that in the wet years. In the case of close annual precipitations, the land use structure is altered, including a decrease in paddy areas and an increase in pond areas, as the water demands for aquaculture and agricultural irrigation increase and that for rice decreases. This tendency is especially apparent in the dry years. Figure 6: Water demands for three types of land use in the (**a**) April-May and (**b**) June-October periods of representative wet and dry years. Figure 6a shows the water demands in spring (April-May period) for the three different land use types; here, the water demand for dryland is indicated as non-existent. The paddy area in 2010 was smaller than that in 1998 for the wet years, but the water demand for paddy during the former period was high.