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Precipitation Spatial Average

Shielded rain gauge at DCEW
Shielded rain gauge at DCEW.

Problem

Precipitation estimates over large areas are needed for many purposes, yet precipitation is typically only measured at points in small buckets. How do we estimate the spatial average precipitation for a large area using point measurements?

Goal

The goal of this exercise is to calculate the total annual depth of precipitation in the DCEW by averaging weighing bucket gauge data from meteorological stations using the hypsometric method, Thiessen polygons, and direct averaging.

Learning objectives

Upon completion of this exercise, students will be able to:

  • Describe the weighted average approach for estimating the average precipitation over a watershed from multiple gauges
  • Obtain weight factors using hypsometric, Thiessen polygon, and direct average methods
  • Construct Thiessen polygons
  • Construct a hypsometric function from a histogram of elevation data
  • Develop a mathematical equation expressing the relationship between precipitation and elevation
  • Combine a hypsometric function with a precipitation-elevation relationship to produce an elevation weighted average precipitation depth

Project Files

Requirements and Connections

  • This exercise requires historical hourly precipitation data collected from meteorological stations at varied elevations within DCEW.
  • Products of this exercise may be used by the Watershed Water Balance exercise.
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