Apex model includes nine modules: meteorology, hydrology, water erosion, nutrient, soil temperature, crop growth, cultivation, crop environmental management and economy. The improved SCS Runoff Curve number method is used to estimate the daily runoff of the model. The original SCS model provides the Runoff Curve Number with a slope of about 5%. The modified Runoff Curve number can be used for other slopes. At the same time, the daily runoff curve number is adjusted according to the soil moisture content and its distribution. Must equation is used to simulate water erosion, which is improved by musle. The biggest difference between must and USLE is that runoff and peak velocity are used as erosivity indicators to simulate soil erosion and sediment yield. This not only improves the prediction accuracy, but also avoids the use of sediment transport rate, but also can be used for sediment yield estimation of word rainstorm.

High resolution land data assimilation system (hrldas) is an off-line driving force of land surface model existing in weather research and prediction (WRF) model. Hrldas uses a combination of observational and analytical measurements (precipitation, solar and longwave radiation, and surface wind, humidity, and temperature) to drive land surface models to simulate the evolution of land surface conditions (e.g., soil moisture and temperature, snow, etc.). The system has been developed and can run on the WRF domain or multiple site locations.

Glims model is jointly developed by University of Georgia and USDA-ARS, its predecessor is creams, which is mainly used for small-scale simulation. The water quality items that can be simulated include sediment, nitrate nitrogen, ammonia nitrogen, phosphorus nitrate, ammonia nitrogen, total nitrogen, total phosphorus, etc. The modified SCS curve number method was used to simulate rainfall runoff, and the priestly Taylor or penman Monteith method was used to simulate evaporation. By simulating the effects of ammoniation, nitrification, denitrification, volatilization, absorption and fixation, the nitrogen factor was simulated by combining empirical or semi empirical formula with the model. A long-term soil erosion model developed by Sharpley et al. Was used to simulate phosphorus. The pesticide composition was mainly aimed at the interaction of pesticide characteristics, soil texture, climate impact, management strategy, surface runoff leakage and adhesion. The model also simulated the pesticide transport in the rhizosphere.

LSPC is a watershed modeling system, including streamline hydrological simulation program FORTRAN (HSPF) algorithm, which is used to simulate hydrology, sediment and general water quality on land, as well as simplified river transport model. LSPC is derived from the mining data analysis system (MDAS) developed by the U.S. Environmental Protection Agency's zone 3, and is widely used in mining applications and TMDLs. A key data management feature of the system is that it uses Microsoft Access database to manage model data and weather text files to drive simulation. The system also includes a module to assist TMDL calculation and source allocation. For each model run, it will automatically generate a comprehensive text file output of the sub watershed for all layers, arrival and simulation modules, which can be represented at hourly or daily intervals. The output of the LSPC is associated with other model applications, such as EFDC, wasp, and - qual-w2. LSPC has no inherent limitations in modeling scale or model operation. The Microsoft Visual C + + programming architecture allows seamless integration with modern, widely used software such as Microsoft Access and excel.

Calite model is an interactive screening model planned and managed by the state water project (SWP) and the Central Valley Project (CVP) in California. It simulates the hydrology of the Central Valley, reservoir operation and delivery allocation decisions to SWP and CVP, delta salinity response to changes in river flow and outlet, and resident ecosystem index. The power of filtering models like callite is the ability to quickly simulate system operations and merge changes relatively easily. The current version of calite simulates the operation of the system on a monthly basis. On the latest modeling computer, it takes about 6 minutes (compared with 30 minutes of calsim), recording a full 82 years of records (water year 1922-2003). Scenarios can be run using a variety of different user specified parameters related to hydrometeorology, requirements, facilities and infrastructure, regulations, and system operations. Through the integrated post-processing tools of the model, we can observe, compare and analyze the results.