In this paper, we evaluate the performance of 19 coupled general circulation models (CGCMs) in twentieth‐century simulations of the Sahel during the 1970s to 1990s. Correlation, regression, and cluster analyses are applied to observations and model outputs including Sahel monthly precipitation, evaporation, soil moisture, and sea surface temperature (SST). We find that only eight CGCMs (hit models) produce a reasonable Sahel drought signal, while seven CGCMs (miss models) produce excessive rainfall over the Sahel during the observed drought period. Even the model with the highest prediction skill of the Sahel drought could only predict the increasing trend of severe drought events but not the beginning and duration of the events. From analyses of the statistical characteristics of the hit and miss models, we conclude that a good simulation of the Sahel drought requires (1) a strong coupling between Sahel rainfall and Indian Ocean SST, with warm (cold) SST identified with Sahel drought (flood), (2) a significant coupling between Sahel rainfall and the Atlantic Ocean SST, with a warm equatorial Atlantic and cold extratropical North Atlantic coexisting with Sahel drought, and vice versa, and (3) a robust land surface feedback with strong sensitivity of precipitation and land evaporation to soil moisture. These three characteristics constitute sufficient conditions for a good simulation of Sahel drought in CGCMs.

Water requirement is sensitive to the impacts of climate change, especially in Bangladesh because of limited freshwater availability in the dry season, despite the fact that the country's agriculture sector requires large quantities of water for the crop production. Hence, gaining a better understanding of changes in water requirements in Bangladesh during dry periods is important in the management of agricultural water resources. This study assesses the recent impacts of climate change on the design water requirement (DWR) of the Boro rice-growing season in Bangladesh using a frequency analysis over a 5-year period. The reference evapotranspiration (ET ref ), crop evapotranspiration (ET p ), effective rainfall (ERF), and gross irrigation water requirements (GIWR) of Boro rice were estimated based on daily weather data for the period of 1984-2013 using the CROPWAT8.0 model. The results showed the significant decreasing trends of ET ref in most of these Boro rice growth stages in all districts. The GIWR of Boro rice and its trends demonstrated significant spatial heterogeneity in the last three decades due to significant changes in the ERF and ET p . The DWR of Boro rice-growing season also supported the results of the GIWR, and the Weibull probability distribution function (PDF) is found to be an optimal PDF among eight PDFs for the estimation of DWR. Overall, the results indicate that a recent climate change does not only contribute to high water demands for the crop but also result in decrease water requirements due to variations in wind speed, sunshine hours, and relative humidity.

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Plant color landscape plays an important role in improving the quality of visual landscapes, regulating the emotion of landscape space, and highlighting the characteristics of urban landscapes. How to reasonably quantify and create rich plant color landscapes to achieve the best visual perception of the plant color landscape at different visual scales, so as to better meet the aesthetic needs of the public, has become a hot and difficult issue in the plant color design and application. Therefore, this article selects four typical urban parks in Nanjing to study the color characteristics of plant communities. The natural color system color card is used to extract plant color data. The color harmony and suitability degree of the plant community and external environment are quantitatively evaluated according to the Moon‐Spencer (M‐S) color harmony theory. The correlation between the chromaticity difference, color harmony, and color suitability of the plant landscape color is strong, whereas that between the chromaticity difference and lightness difference of the plant landscape color is weak. Among the four urban parks, the color harmony is the highest, and the appropriate color is the lowest in Xuanwu Lake Park. In addition, among the 12 selected plant community landscapes, the plant community number A3 in Xuanwu Lake Park has the highest color harmony and D3 in Gulin Park has the lowest color harmony. In short, the quantitative study of the plant community landscape color can provide new ideas for improving the optimal allocation of the plant community landscape color in urban parks.