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Databases
CLIMWAT 2.0 for CROPWAT

CLIMWAT is a climatic database to be used in combination with the computer program CROPWAT. and allows the calculation of crop water requirements, irrigation supply and irrigation scheduling for various crops for a range of climatological stations worldwide.

CLIMWAT 2.0 for CROPWAT is a joint publication of the Water Development and Management Unit and the Climate Change and Bioenergy Unit of FAO.

CLIMWAT 2.0 offers observed agroclimatic data of over 5000 stations worldwide distributed as shown below.

Stations in CLIMWAT 2.0

Location of stations included in CLIMWAT 2.0.

CLIMWAT provides long-term monthly mean values of seven climatic parameters, namely:

  • Mean daily maximum temperature in °C
  • Mean daily minimum temperature in °C
  • Mean relative humidity in %
  • Mean wind speed in km/day
  • Mean sunshine hours per day
  • Mean solar radiation in MJ/m2/day
  • Monthly rainfall in mm/month
  • Monthly effective rainfall in mm/month
  • Reference evapotranspiration calculated with the Penman-Monteith method in mm/day.

The data can be extracted for a single or multiple stations in the format suitable for their use in CROPWAT. Two files are created for each selected station. The first file contains long-term monthly rainfall data [mm/month]. Additionally, effective rainfall is also included calculated and included in the same file. The second file consists of long-term monthly averages for the seven climatic parameters, mentioned above. This file also contains the coordinates and altitude of the location.

All station information is drawn from the database of The Agromet Group of FAO.

All variables, except potential evapotranspiration, are direct observations or conversions of observations.   Original data coming from a large number of meteorological stations as included in CLIMWAT, could not be uniform.  For example, humidity and radiation can be expressed through different variables. With respect to humidity, data can be provided as relative humidity, dew point temperature or water vapour pressure. These three variables can be uniquely converted into each other if the mean temperature is known. However, if humidity is measured and provided in more than one of these variables, the actual numbers would not necessarily be in line. In this case it is necessary to decide which variable to use. When compiling CLIMWAT, it was decided to use water vapour pressure as a core variable and only where it is not available, use dew point temperature and relative humidity. However, there is a risk that the provided value of vapour pressure is higher than the one that is possible to obtain, given the mean temperature. The original databases were crosschecked for this possible inconsistency and one of the other variables was used in the few cases where it occurred.

The same problem arises with radiation. Instead of the solar energy flux at the surface often only sunshine hours or sunshine fraction are recorded, both of which though can be converted to radiation. In order to calculate evapotranspiration using the Penman-Monteith method, both radiation and sunshine fraction are necessary. To keep both these values in agreement the observed radiation was used as base variable and the sunshine fraction was estimated from it. When only the sunshine fraction (or hours) has been observed it was used to estimate radiation. If both (fraction and radiation) are observed radiation was preferred.

As a result, the provided relative humidity and sunshine hours are often deduced from observations of vapour pressure and radiation, even if the former are observed. The procedure, however, ensures that the different expressions are coherent.

In compiling the data, an effort was made to cover the period 1971 - 2000, but when data for this period were not available, any recent series that ends after 1975 and that has at least 15 years of data have been included.  Some of the series are "broken", but they nevertheless have at least 15 years of data (e.g. 1961-70 and 1992-2000).

We prepared the dataset and the extraction software with great care and made every effort to provide reliable data. However, we cannot guarantee that all the observations that went into the procedure are free of errors.

 

 
   
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