WaterWare:   Lerma-Chapala, Mexico

Rainfall in this part of Mexico normally occurs only for 3 or 4 months of the year, the remaining period being warm and dry. When rainfall does occur, it is mainly associated with thunderstorms, and flooding is a common problem. As this is a semi-arid area, agriculture is reliant on irrigation, which annually accounts for nearly 5,500 million cubic meters of water. Groundwater is also used for irrigation but there are no major aquifers in the Lerma valley, only infilled-lake sediments.

The rainfall runoff model (RMM) is a daily, lumped parameter water budget and runoff model for small and medium-sized sub catchments. It obtains its input data from the river basin objects and their associated precipitation, temperature, and runoff data.

RRM provides its main output (time series of daily runoff data) also in a file format that is compatible with the WRM Water Resources model RRM can therefor be used as a pre-processor for WRM, generating flow data for start-nodes, as well as a stand-alone model for sub-catchment analysis. By adding lateral inflow and outflow to the current model, so that a number of sub-catchments can be combined into a larger unit, a spatially distributed model with a hydrologically oriented rather than purely geometric (regular grid) resolution can easily be realised.

RRM is designed to:

  1. Provide a dynamic, daily water budget and runoff data for ungauged catchments, using observed or synthetic meteorological data (precipitation, temperature);
  2. Evaluate the effects of conjunctive surface water and groundwater use through the effects of groundwater extractions (from single or two layer aquifer systems) on the baseflow component of the runoff;
  3. Evaluate the effects of landuse change on runoff including the baseflow and groundwater recharge components.
The main processes the model considers are evaporation and evapotranspiration, surface runoff, interflow, routing to and through the channel system and deep percolation that contributes to the groundwater storage and ultimately the baseflow.

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