Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2002
Publication Date: 6/20/2003
Citation: Zhang, X.C. Assessing seasonal climatic impact on water resources and crop production using CLIGEN and WEPP models. Transactions of the American Society of Agricultural Engineers. 2003. v. 46(3). p. 685-693. Interpretive Summary: Computer models of water movement and vegetation growth, called response models, are useful tools for assessing the impact of different climate conditions on water resources and plant growth. Most response models require daily weather input, which can be generated using a climate generation computer program. The objectives of this work are to evaluate the ability of the CLIGEN (a climate generator) model to reproduce daily weather and to assess the movement of water and crop productivity responses to different climate conditions using the Water Erosion Prediction Project (WEPP) model. The CLIGEN model was evaluated at four Oklahoma weather stations, and was then used to generate 'typical' climate conditions that mimic wet, dry, and average year conditions for the Chandler, OK, site. The WEPP model was run for the generated climate conditions. CLIGEN satisfactorily generated daily and monthly precipitation, and daily temperatures, and was capable of reproducing different climate conditions. Application of WEPP to different climate conditions showed that winter wheat grain yield increased 0.5 to 0.8 fold for one fold increase in average growing-season precipitation, and the rates of the increase were greater under drier initial soil moisture conditions. Results indicate that CLIGEN, when used with response models such as WEPP, provides an effective tool for evaluating crop response to climate variations and for analyzing production risks for any given cropping system and seasonal climate forecast. This information will help farmers and extension professionals make better and informed planning and management decisions.
Technical Abstract: Physically based response models are useful tools for assessing impacts of climate variations on hydrological and plant growth processes. Most response models require daily weather, which is often synthesized using stochastic daily weather generators. The objectives were to evaluate the ability of the CLImate GENerator (CLIGEN) model to generate various climate scenarios and to assess the hydrological and crop productivity responses using the Water Erosion Prediction Project (WEPP) model. CLIGEN was evaluated on four Oklahoma weather stations, and was then used to generate 'typical' climate scenarios that represent wet, dry, and average year categories on the Chandler, OK, site. The calibrated WEPP model was used to simulate hydrologic and wheat grain yield responses to the generated climate scenarios. Results show that monthly precipitation was well simulated by CLIGEN, but daily precipitation was less well reproduced. For applications like crop forecasts, preservation of monthly precipitation is more relevant. CLIGEN was capable of preserving statistics of monthly precipitation as well as reproducing seasonal precipitation patterns for the three year categories. Predicted percent increase of wheat grain yield per 1% increase of precipitation, which was a function of initial soil moisture storage and total precipitation, ranged from 0.5 to 0.75%. This study demonstrated that CLIGEN, when used in conjunction with response models such as WEPP, can provide a useful tool for assessing the impact of seasonal and interannual climate variations derived from probabilistic type of climate forecasts. More importantly, CLIGEN has the potential of downscaling monthly climate forecasts to daily weather series while preserving the statistics of the forecasts.