Precipitation measurement and the analysis of hydrological resources in a river basin

Arminda Manuela Gonçalves 1 and Teresa Alpuim 2
1 Department of Mathematics for Science and Technology, University of Minho, 
Campus de Azurém 4800-058 Guimarães, Portugal
Tel.: +351 253510433; Fax: +351 253510401
mneves@mct.uminho.pt
2 Department of Statistics and Operations Research, University of Lisbon
Campo Grande, Edifício C5, 1148-016 Lisboa, Portugal
Tel.: +351 21750047
mtalpuim@fc.ul.pt 

Abstract
The spatial and temporal measurement of precipitation on a geographical area, is essential when calculating hydrological balance for the indirect estimation of water flow and for the development of the study of the watershed charge. It is also very important for modelling many environmental phenomena, for example the variation of the water quantity of a hydrological basin of a river. The quality of water, in a certain location, is the reflex of the dominant conditions in the source basin of that location, namely the hydro-meteorological factors. The variation of a spate-time quality variable is associated to the variation of the flow (variable dilution effect) which in term is related, in general, to the seasonal variation of rainfall. We present the problem of area precipitation  measurement in order to estimate a hydro- meteorological factor that will be used in the modelling of the surface water quality of river basins. In our study we need monthly measurements of rainfall averages in area, which influence a certain area of the River Ave basin (located in the north-west of Portugal) and which represent the hydro-meteorological factor in the modelling of the quantity of water. Our main goal is to identify models which estimate well monthly average rainfall in places where there are no observed values (in the monitoring points of quality of water), with the help of the spatial distribution of the rainfall and measurements in other locations. Due to the large space and time variability of rainfall, the precise evaluation, in real time, of mean area estimates poses a difficult problem. These estimates are obtained from a set of rain gages, located at 19 points in the area of the Ave River hydrological basin. We estimate the monthly values of rainfall per area flowing into each monitoring site. To accomplish this, we propose a methodology combining both deterministic (Thiessen’s polygons) and  stochastic (Kriging) processes.

Keywords: hydrological basin, hydro-meteorological factor, area rainfall estimation, Thiessen’s polygons, Kriging

In: Caetano, M. and Painho, M. (eds). Proceedings of the 7th International Symposium on Spatial Accuracy Assessment in Natural Resources and Environmental Sciences, 5 – 7 July 2006, Lisboa, Instituto Geográfico Português

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