ERS 60

Problem Set 2

Energy balance and water balance on landscapes and in soils play an important role in determining the types of vegetation that occur, the amount of energy and water available for soil formation, and the amount of water available for aquifer recharge and stream runoff. Energy dissipation by evapotranspiration (evaporation from soil plus transpiration by plants) affects the amount of water that can be stored in soils. A water balance is dependent not only on the magnitude of precipitation (P) and evapotranspiration (ETp), but on the timing, or seasonality, of precipitation and solar radiation. The water balance used here is sometimes called a "bucket model". The soil is the bucket that can hold a maximum amount of water (water holding capacity). The bucket can be filled when P exceeds ETp, or emptied when ETp exceeds P. Storage can never be less than zero because the bucket is empty. Also, once the bucket is full, an excess of P over ETp produces a surplus (the bucket overflows) that can contribute to leaching of soils, recharge of groundwater aquifers, and streamflow. Refer to chapter 9 in the text for a discussion of water balance.

PART 1:

Using the average climatic data below (P and ETp in cm) for three weather stations, calculate and graph a water balance for each location (plot evapotranspiration and precipitation vs. months of the year). Based on the water holding capacity (WHC in cm) of the soils given, show areas of Recharge (R), Utilization (U), Deficit (D), and Surplus (S). Note that surplus and deficit do not accumulate from one month to the next, but that storage does, until soil water holding capacity is exceeded. Note that ETp refers to potential evapotranspiration, not actual evapotranspiration.

PART 2:

Based on the climatic data and water budgets, identify the most likely Köppen system climate designation (e.g., Dwa, BSh, EF, see chapter 10), and make your best guess as to where on the globe these climatic stations are located. For each location, in 25 or fewer words, justify your choice.