[Effect of meteorological factors on design farmland drainage modulus.]

Calculation of design drainage modulus is of great importance for the safety of farmland and reduction of waterlogging loss. We investigated the effects of main meteorological factors on design farmland drainage modulus by focusing on a closed farmland area in Ninghe District of Tianjin City. To resolve the problem of limited observation, the parameter sensitivity was analyzed according to mutual information and partial rank correlation coefficient aiming at the total runoff depth based on field observation experiment. The reasonable parameters were obtained by combining with soil water content and the relative variation of groundwater level. Then, a three-source runoff yield model coupling of excess infiltration and saturation was established to estimate runoff and design drainage modulus, and the effects of meteorological factors such as precipitation and evaporation on drainage modulus were analyzed. Results showed that summer precipitation significantly reduced and evaporation varied a little during 1960-2015. The corresponding drainage modulus decreased with the reduction of precipitation. When return period increased, the magnitude of the reduction in precipitation as well as the design drainage modulus increased. However, the effects of meteorological factors on design drainage modulus was generally inapparent. Thus, we concluded that the current drainage modulus is suitable for the study area.