The mayor recharge in the the south of the peninsula of Baja California has its origin at “La Sierra de la Laguna“, a mountainous hill in the center which was build by metamorphic rocks and reaches up to 2100 m above sea level. The precipitation rate in the highest parts of this hill reaches 700 mm in an average year which is equal to the potential evapotranspiration.

The water flows down the mountains and infiltrates in the subsequent alluvial fans and recharges the aquifers. Another important factor in the water balance of the region are the very intensive rainfalls caused by tropical storms like hurricanes. We observed the effects of the hurricane Juliette, that affected the area from September 26th to October 1st 2001. A maximum rainfall of 1100 mm was observed at the “Caduaño“ meteorological station (180 m above sea level), which was the highest precipitation ever observed in the south of the peninsula.

After the hurricane we started to install a net of hydrometrical stations around the hill and measured the runoff in 11 catchment areas with a total of 1800 km² until April 2002. Depending on the relation between metamorphic rocks and unconsolidated sediments forming the catchment areas, up to 18 percent (in average 4,9 % ) of rain recharged the aquifers and was measured as base flow. At the moment we are installing an net of observation wells to measure the flow of ground water and the superficial flow continuously within the next years.