INTRODUCTION 
The attitude to water problems is changing. A number of products which have 
been found suitable in connection with water resources planning for a long 
succession of years have exhausted their usefulness, others have come to re- 
place them. The hydrological information we can give in future will to a great 
extent be based on hydrological models of different types. We will further use 
digital map information and satellite images. Modern computer techniques allow 
automatic production of maps and diagrams in colour as well as on line display 
of such information. Geo-coded data bases will be of great importance. 
The most widely used models in hydrology today are lumped models, but they do 
not answer sufficiently to the present needs of hydrological information for 
water resources planning. The present needs of water information calls for a 
new generation of distributed hydrological models. Hydrological and climato- 
logical observations are seldom of sufficient density in space to provide the 
wished basic information for the distributed models. However new types of 
digital data sources are available for supplementary landscape information and 
these data sources can be used to refine the models. 
The point of departure for all types of hydrological information is a hydro- 
logical, climatological and ground water observation network. Some or all of 
the watershed characteristics listed in the table below are required for most 
hydrological models. 
  
  
Surface water Meteorology 
Stream discharge Rainfall 
Lake and reservoir level Temperature 
Water temperature Humidity 
Sediment concentration Barometric pressure 
Chemical and biological Radiation 
properties Sunshine duration 
Evaporation 
Snow depth and water content 
Interception 
Watershed caracteristics Soil and groundwater 
Topography (drainage area Water level 
and land slopes) Temperature 
Geology Chemical properties 
Soil type Storage coefficient 
Geomorfology (drainage Permeability 
pattern) Moisture content 
Vegetation 
Land use 
One of the main areas of application is in regional analyses in which selected 
characteristics are related to different hydrological variables. Selected 
characteristics are also used in most lumped conceptual models of the rainfall- 
runoff process. Distributed hydrological models are to a still higher degree 
dependent on watershed characteristics.Often today the information needed is 
not readily available, and the modeller is frequently forced to use a more 
simple model. 
Normal derivation of watershed caracteristics is laborous, time consuming and 
costly. New data sources like Landsat imagery and digital map data opennew 
fields for hydrologic model development. The way digital map information can 
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