be used for hydrological application are related to the purpose for the infor- 
mation to be used. We shall differ between 
ve - Comprehensive hydrological information covering the whole country. 
ig - Detailed hydrological information for a region. 
re- 
great COMPREHENSIVE INFORMATION 
r use 
allow The aim with the comprehensive information is first of all to identify the areas 
splay with similar conditions, both favourable and unfavourable. Here it is important 
that the presentation should be done in such a way that the comprehensive 
information easily can be combined with other general information on a national 
y do level. À suitable computational element in Sweden is the one applied in the 
for Physical National Planning data bank, i.e. the Economic Map sheet (5 km square). . 
r a Suitable map scales for the presentation of this information are scales 
ito- 1:1 000 000 and 1:2 000 000. 
the 
f In the comprehensive mapping we use hydrological models first of all to transmit 
n and information from observation points to the computation elements (ref./2/ and /3/) 
Geographical conditions can in this case be given in simplified form. Land use, 
vegetation, soil type and geology are classified and the characteristics for 
Iro- each element are given as the percentage of each class present. Landsat data is 
of perfect for this application. The advantages are: 
most - More 'up-to date' information, due to continuity in the Landsat-data and 
thus possibilities to follow changes in land-use in time and space. 
- More rapid data acquisition. 
- Greater precision in the land-use concept due to the greater number of 
land-use classes. 
- Possibly more detailed information due to the smaller grid intervall ( in 
95 percent of cases the errors will be less than 0.02 for diments 5 km square) 
  
However topography and geomorphology can today not be evaluated from Landsat- 
data. 
intent REGIONAL INFORMATION 
The management aspect is the important one at regional level. The point is to 
effectively utilize and maintain the water resources within a region. Infor- 
mation should be related to actual points in rivers and lakes. The element 
forming the basis of calculations should necessarily be the watershed and not. 
a more general unit, e.g. 5 km squares or administrative units (/4/) A suit- 
able size for the catchment as a computational element is 50 - 200 km“. In- 
formation necessary for water management planning at a regional level is the 
size of the different water balance elements, runoff, soil and ground water 
storage, precipitation and evaporation for each unit. Transport times and 
residence times within and between subcatchments are also important factors 
when we want to combine hydrological variables with hydrochemical and ecological 
ones. Without a clear understanding of the runoff formation processes within 
ected a basin's different parts, the procedure of forecasting the hydrological events 
| remains at the level of temporary engineering solution, satisfying strictly 
nfall- limited needs and preserves the character of a guessing game though the results 
ree can be quite satisfactory for a particular application. Heterogenity in the 
|. is runoff format within a watershed calls for a model which takes into account 
‘€ basin caracteristics. 
Distributed hydrological models are based on spatially distributed input. As 
| and hydro-meteorological observation nets 'cannót provide thé required density of 
ew observations to describe watershed's heterogeneity, remote sensing and alter- 
can native inputs should be considered. In this paper we limit ourselves to the 
discussion of the Landsat imagery applications to obtain land use data for 
regional hydrological modeling and planning. 
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anal ^ s 
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