IAHS  MAASTRICHT ASSEMBLY Workshop W 4 / 19 - 20 July 2001


Some essential conclusions ( strongly condensed , compiled by H.Lang, Convener including various input from chairmen and CoConveners) :


1. A General Comment

The very great significance of mountain regions snow, ice and water, for the water supply of large continental areas and for the flow regimes far downstream of many of the worlds large rivers deserves much more and broad attention.

With view to future climatic scenarios and their impacts on the water cycle, the scientific research in the fields of Mountain Hydrology, Glaciology and Ecosystems should be given high levels of priority.Specific attention should be given to the less developed mountain regions.

The scientific approaches need to be interdisciplinary, and a particularly strong interconnection of hydrological sciences is needed with the atmospheric/climatic science communities and with the ecosystem groups (such as IGBP/BAHC Mountain Initiative).- It should always be kept in mind that more or less most of the "natural" variations in time of hydrological fluxes are controlled and caused by atmospheric dynamics and radiative
processes.


2.More specific output from the seven W 4 Sessions :

--The orographic control of precipitation amounts and distribution in high mountain regions is still an outstanding problem in the reliable assessment of P by observation networks and in model approaches. And there is still great uncertainty in the altitudinal gradients of P.
International field- and model experiments like the Mesoscale Alpine Project MAP
(SOP 1999, European Alps) are of particular importance to improve our understanding and in developing advanced scientific and practical tools.

--Besides their great significance in the global climate system the variations in the cryosphere (a huge and complex storage and release system in time scales of between days and millenia of years) need careful monitoring and model efforts also with view to their effects on the sea
level variations.Promising model approaches are in development to estimate the global glacier mass balance ( 15 to 20 % of present days sea level rise is caused by the mass loss of mountain glacier systems). However there are regions where at the same time glaciers show positive mass balances which indicates the great complexity of the combined ocean-landsurface-atmospheric climatic systems, which reminds us that the present increase of annual mean air temperature is only one part of the climate change signal.Present days hydrological and cryospheric model developments as shown in the sessions are more and more well physically based and can therefore handle non-stationary developments much better. Under these aspects the worldwide monitoring and data collection efforts deserve in
their great importance also to be mentioned here.

-- In the USA a new NASA program is on the way to refine remote sensing techniques.

--One session was devoted to tropical glaciers and mountain hydrology showing up the great and different from mid latitude complexity of glacier behaviour under the tropical climatic conditions.

--It was made clear that any change in the areal disribution, extent and length of glaciers and of winter snow cover will affect the variability and regime of  the downstream river flow with corresponding consequences for the availability of water for water supply and reservoir management. In addition it will also affect the frequency and severeness of extreme hazards
i.e. floods and dry periods.