Irrigated agriculture is the largest water user in many regions, and agricultural water use efficiency and consumption has been studied by several authors. This paper provides a framework and application of economic valuation of water for agriculture in three regions in northern Baja California, Mexico, namely Guadalupe, Maneadero and Mexicali Valleys. Positive mathematical programming (PMP), a deductive valuation technique, was the framework used for this estimation using water delivery data reported by the National Water Commission in Mexicali, production costs and cultivated area, production factors use from the Agriculture Ministry (SAGARPA); and other data from previous studies. Analysis of the results shows that marginal economic water value in Mexicali is at least 2.6 times the water price paid by farmers. Guadalupe and Maneadero with higher value agriculture, have higher marginal economic values of water than Mexicali, albeit closer to their water costs. Small shortages increase this economic value for farmers. Estimated price elasticities of irrigation water for each turn-out are inelastic for all regions and within the range of most previous studies. Policies aimed to reduce water consumption by decreasing current pumping subsidies are encouraged.

In order to recognize the soil and geomorphologic characteristics of the northeastern part of Valle de Guadalupe, Baja California, and its implications on the runoff volumes in the region, 59 soil samples were collected from the first 5 cm of the soil layer, taking into account the surface relief, soil classification and vegetation cover of each sampling point. Soil moisture content and textural analyses were carried out in the laboratory for each sample. Three raster images were used to complement field data: an Ikonos image, an Aster Image and the Instituto Nacional de Estadística Geografía e Informática digital geologic map I11D82. The Ikonos image was used to calculate the normalized differential vegetation index, the Aster image to evaluate the field slope, and the digital map to obtain geologic information for the study area. Following the runoff curve number method, a computational algorithm was developed (for Ermapper 6.4 software), by using the three raster images and the field data. The algorithm was employed to study the surface runoff potential in the Serranía Matcuatai and to evaluate its runoff volume contributions to Valle de Guadalupe. The mean annual runoff volume contribution was estimated in 258,000 ± 123,000 m³. It was also found that 88% of the study area surface has a runoff potential and only 12% is favorable to infiltration.

The amount of sediment drained into the Pacific coast due to the orographic system of northem Baja California was estimated by indirect methods. Langbein and Schumm’s (1958) equation was used to relate the erosive action of the rain and the protective action of the vegetation. Statistics on pluvial precipitation for 1950 to 1983 of 21 stations of the Secretaria de Agricultura y Recursos Hidráulicos were used. Furthermore, topographical data of 44 charts of the Instituto Nacional de Estadística, Geografía e Informática (INEGI), corresponding to the northem area of Baja California, were digitized on a PRIME 750 computer and processed with a program (TOPOGRAFIC) developed at the Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE). Two drainage basins were identified as maximum potential sources of sediment: the Tijuana River basin (S = 809649.88 tons/year) and the Guadalupe River basin (S = 834889.13 tons/year). According to the model, these are not maximum values. Higher values can be expected with greater rainfall and we thereforeconsider this area to be one of high geological risk.