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Water and energy budget of the Ohrid Lake basin for 1990:

Part A) Water and energy budget of a land site near the lake – the Ohrid meteorological station;. Water and energy budget of the Ohrid Lake basin for 1990:. Part B) Estimation of the lake monthly water budget for year 1990;.

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Water and energy budget of the Ohrid Lake basin for 1990:

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  1. Part A) Water and energy budget of a land site near the lake – the Ohrid meteorological station; Water and energy budget of the Ohrid Lake basin for 1990: Part B) Estimation of the lake monthly water budget for year 1990; E. Artinyana, O. TodorovikbaNational Institute of Meteorology and Hydrology, BAS139 Ruski bld., 4001 Plovdiv, BULGARIAbHydrometeorological Service of MacedoniaSkupi bb, 1000 Skopje, MACEDONIA

  2. Objectives: • To ascertain the energy and water budget of a land site near the lake for one year • To evaluate the monthly water balance of the Ohrid lake • next work: water and energy budget of lake’s surface water basin Methods: • Physically based, single column land surface scheme -ISBA • Physically based, single column dynamic reservoir simulation model DYRESM

  3. Needed data: • Atmospheric forcing needed both by ISBA and DYRESM • Air temperature, wind speed, air humidity, atmospheric pressure, global solar radiation, long wave atmospheric radiation, liquid and solid precipitation • Water temperature as additional forcing is provided to ISBA • Vegetation and soil properties used by ISBA • Veg, LAI, z0, albedo, SAND and CLAY percentage, depth of the soil column, rooting depth • Water body morphometric information needed by DYRESM Sources of data: • Atmospheric forcing – Hydro-meteorological service of Macedonia • Clear sky solar radiation from ESRA clear sky model • Monthly water level and water temperature from WOISYDES web site • Vegetation and soil properties – ECOCLIMAP database (Météo France) • Bathymetric map – published by Sinisha Stankovik (1959)

  4. Monthly means of the atmospheric forcing for Ohrid meteorological station : Air temperature, air relative moisture, wind velocity and precipitation Global solar radiation, Long wave atmospheric radiation The values are used after checking and error correction The values are computed. Global radiation is computed with respect to heliosat method ( ESRA model).

  5. ISBA land surface scheme Takes input forcing from the atmosphere Uses: 3 layer snow pack 3 layer soil representation Computes energy fluxes at the screen level: latent heat of evaporation turbulent heat flux ground heat flux Output: Evaporation from vegetation and bare ground; surface runoff and drainages fluxes

  6. Part a) Results for the land site: Monthly energy budget Monthly water budget RN: net radiation flux ; H: turbulent heat flux; LE: latent heat flux [W/m2] RR: precipitation; runoff; drainage; evaporation; DL: ground storage [mm]

  7. Part b) Monthly water budget of the lake for 1990: Known terms: • Og: underground outflow is assumed to be null • Os: the only outflow from the lake is the Crn Drim river discharge at Struga that is measured Computed terms: • P: available coast line station precipitation data are used to compute the monthly precipitation over the lake surface. • E: DYRESM model is forced with data from the meteorological station assuming equal inflow and outflow. It computes the water level variation, which is equal to the evaporation (minus precipitations). • dVL/dT: Lake volume variation is derived from water level variation and lake’s morphometry (volume-level curve) (Rozanski et al. 2000) Remaining terms: • IG and IS: underground and surface inflow

  8. Part b) Results: I: total inflow (blue-green) [mm] P: precipitation (green) [mm] E: evaporation (red) [mm] O: outflow (dark blue) [mm]

  9. Conclusion Part a) In the first part the land site energy and water budget are established. The result shows typical Mediterranean climate pattern. Most of the solar energy is returned to the atmosphere by turbulent heat flux as not enough water for evaporation is available during the vegetation growth. Drainage and surface flow occur mostly in winter time when precipitations are higher than the sum of evaporation terms. Part b) The monthly water budget of the lake is computed using a simplified balance equation. The term of lake open water evaporation is estimated with respect to the cooling effect of precipitations and inflow water temperature. Monthly total inflow into the lake is evaluated as the only unknown term of the balance equation. Monthly underground inflow could be estimated after comparing those results with the measured surface inflow into the lake.

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