Presentation on theme: "Topics for 9/6 Annual water balance and the Budyko curve"— Presentation transcript:
1 Topics for 9/6 Annual water balance and the Budyko curve Project progress
2 Water Balance Ratios can be used to “characterize” watersheds Q/P, ET/P…Energy limited vs Water limited systemsBudyko (1974) Climate and Life
3 Physical Controls on Water Balance at Catchment Scales Treat as a lumped systemReceives rainfall at the rate p(t), loses water through evapotranspiration e(t), and runoff q(t)dS/dt = p(t) – q(t) – e(t)Where S is the storage of water at any time (t)At the annual scale we assume there is no carry over from year to year andP = Q + E where P, Q, and E are annual totalsWe will investigate the “partitioning” of the water balance at the annual scaleKey Point: Annual water balance is controlled by climate
4 Bucket Model Assumptions p and e are uniform through the yeare occurs at potential rate as long as water is availableNo runoff if bucket is less than full
5 Two Scenarios Case 1: Dry Climate (arid) Ep>P, and ep(t) > p(t) …Actual E is controlled by the amount of rainfallWater limited systemS/Sb= 0No water storage, no vegetation…adverse to life
6 Two Scenarios Case 2: Wet Climate (humid) P>Ep, p(t) > ep(t) What happens to the bucket?E = Ep, Q = P – EpUpper limit to e(t) is the evaporation demandEnergy limitedS/Sb = 1Too wet, adverse to life
7 Budyko Diagram Consider the limits Plot E/P vs Ep/P If E = Ep (wet climate)…If E/P = 1 (dry climate) …E/P is a measure of actual water balanceEp/P is a measure of climate, called dryness index
8 Limits of Budyko Diagram Whole world can be divided in to “energy limited” and “water limited” areasWhy doesn’t empirical curve match theoretical?
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