This paper examines the water budgets of two climatically distinct cities — Berkeley, California, and Terre Haute, Indiana — and explains how geography, climate, altitude, and soil composition drive differences in precipitation, evapotranspiration, soil storage, and deficit. Berkeley's Mediterranean coastal climate produces wet winters and dry summers, while Terre Haute's mid-latitude continental climate yields humid summers and cold, snowy winters with frozen, impermeable soils. Monthly water budget tables are presented for each location, and the contrasting patterns in surplus, deficit, and actual evapotranspiration are analyzed in relation to each city's regional climate controls.
The water budget of a particular area can differ greatly depending on a number of factors. Climate, geographical location, altitude, and soil density can all have major impacts on the water budgets of specific areas. Precipitation is the primary source of water acquisition; as Ritter (2006) notes, "Precipitation in the form of rain, snow, hail, etc. makes up the primary supply of water to the surface." Thus, the climate of individual areas plays a huge role in determining the amount of precipitation received. Climate also governs evaporation: "Actual evapotranspiration increases as temperature increases, so long as there is water to evaporate and for plants to transpire" (Ritter, 2006).
However, climate as determined by geographical location is not the only factor. The actual composition of soil in particular areas will influence how much water that area can retain. According to Ritter (2006), "The amount of water in the soil depends on soil properties like soil texture and organic matter content." Land holds approximately 2.4% of the total water on Earth (University of Illinois, 2010). Soil in each area therefore plays a key role not only in the construction of the water budget, but also in how much water will be evaporated. There are a number of different soil formulations based on the resources and materials present in a given area, and these different formulations retain water at different levels: "Different surfaces hold different amounts of water and absorb water at different rates" (University of Illinois, 2010). With these principles in mind, specific geographical locations can be meaningfully compared.
The monthly water budget data for Berkeley, California (Figure 1) are presented below. Values for precipitation (P), potential evapotranspiration (PE), the difference between the two (P–PE), change in soil storage (Change in ST), soil storage (ST), actual evapotranspiration (AE), deficit (D), and surplus (S) are given for each month of the year.
In comparison to Terre Haute, Indiana's water budget, the primary differences in location and climate explain the contrasts in the figures above. Berkeley sits at 37°52'17.73" N, 122°16'13.86" W, with an elevation of 179 feet above sea level. This keeps it closer to the oceanic controls that regulate coastal temperatures. Berkeley has a west-coast Mediterranean climate, characterized by hot, dry summers and mild, wet winters. The hot and dry summer element has a pronounced impact on Berkeley's water budget during those months, in contrast to the more humid Indiana summers that see frequent storms. As Schaffner and Robinson (2009) note, Mediterranean climates feature "extremely dry summers caused by the sinking air of the subtropical highs," which may last up to five months.
Additionally, Mediterranean climates experience mild winters with little or no snow, so water acquisition depends primarily on rainfall. Berkeley's climate is moderated by the North Pacific High, an oceanic high-pressure cell that keeps temperature ranges moderate. The city lies on the west side of the mountains, so the area receives considerably more precipitation than the drier inland regions (University of Illinois, 2010). Most Mediterranean climates occur on the western ends of continents, and Berkeley — along with the entire California coast — receives the majority of its rainfall during the winter months. Consequently, precipitation rates are highest in winter and fall sharply through the rest of the year. The ocean further regulates temperature in this area, a moderating influence that is entirely absent in the case of Terre Haute, Indiana. Rather, Berkeley is surrounded by the ocean and mountains, and these are the primary factors that produce the differences observed between the two cities' water budgets.
"Monthly water budget data table for Terre Haute"
"Frozen soils and humid summers shape Indiana's budget"
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