WORLD METEOROLOGICAL ORGANIZATION OPERATIONAL HYDROLOGY REPORT No. 42 METEOROLOGICAL SYSTEMS FOR HYDROLOGICAL PURPOSES WMO-No. 813 Secretariat of the World Meteorological Organization – Geneva – Switzerland THE WORLD METEOROLOGICAL ORGANIZATION The World Meteorological Organization (WMO), of which 187* States and Territories are Members, is a specialized agency of the United Nations. The purposes of the Organization are: (a) To facilitate worldwide cooperation in the establishment of networks of stations for the making of meteorological observations as well as hydrological and other geophysical observations related to meteorology, and to promote the establishment and maintenance of centres charged with the provision of meteorological and related services; (b) To promote the establishment and maintenance of systems for the rapid exchange of meteorological and related infor- mation; (c) To promote standardization of meteorological and related observations and to ensure the uniform publication of observations and statistics; (d) To further the application of meteorology to aviation, shipping, water problems, agriculture and other human activi- ties; (e) To promote activities in operational hydrology and to further close cooperation between Meteorological and Hydrological Services; and (f) To encourage research and training in meteorology and, as appropriate, in related fields and to assist in coordinating the international aspects of such research and training. (Convention of the World Meteorological Organization, Article 2) The Organization consists of the following: The World Meteorological Congress, the supreme body of the Organization, brings together the delegates of Members once every four years to determine general policies for the fulfilment of the purposes of the Organization, to approve long- term plans, to authorize maximum expenditures for the following financial period, to adopt Technical Regulations relating to international meteorological and operational hydrological practice, to elect the President and Vice-Presidents of the Organization and members of the Executive Council and to appoint the Secretary-General; The Executive Council, composed of 36 directors of national Meteorological or Hydrometeorological Services, meets at least once a year to review the activities of the Organization and to implement the programmes approved by Congress; The six regional associations (Africa, Asia, South America, North and Central America, South-West Pacific and Europe), composed of Members, coordinate meteorological and related activities within their respective Regions; The eight technical commissions, composed of experts designated by Members, study matters within their specific areas of competence (technical commissions have been established for basic systems, instruments and methods of observation, atmospheric sciences, aeronautical meteorology, agricultural meteorology, marine meteorology, hydrology, and climatology); The Secretariat, headed by the Secretary-General, serves as the administrative, documentation and information centre of the Organization. It prepares, edits, produces and distributes the publications of the Organization, carries out the duties specified in the Convention and other Basic Documents and provides secretariat support to the work of the constituent bodies of WMO described above. ________ * On 30 November 2003. WORLD METEOROLOGICAL ORGANIZATION OPERATIONAL HYDROLOGY REPORT No. 42 METEOROLOGICAL SYSTEMS FOR HYDROLOGICAL PURPOSES WMO-No. 813 Secretariat of the World Meteorological Organization – Geneva – Switzerland 2003 Cover photo: Australian Bureau of Meteorology; WMO. © 2003, World Meteorological Organization ISBN 92-63-10813-7 NOTE The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the World Meteorological Organization concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. CONTENTS Page Foreword . v Summary (English, French, Russian and Spanish) . vii 1. INTRODUCTION . 1 2. METEOROLOGICAL MEASURING AND OBSERVING SYSTEMS . 4 2.1 Conventional measuring networks . 5 2.1.1 Synoptic measuring networks . 5 2.1.2 Climatological measuring networks and hydrometeorological networks . 8 2.1.3 Error sources and measuring accuracy . 9 2.2 Remote-sensing procedures . 10 2.2.1 Radar-based precipitation measurements . 11 2.2.1.1 Measuring procedure . 11 2.2.1.2 Error sources and measuring accuracy . 12 2.2.2 Satellite data for the estimation of precipitation . 13 2.2.2.1 Precipitation intensity from cloud information with visible and/or infrared data . 13 2.2.2.2 Precipitation intensity from microwave data . 14 2.2.2.3 Measuring accuracy . 15 2.3 Combined measuring systems . 15 3. DATA DERIVED FROM METEOROLOGICAL MEASUREMENTS . 17 3.1 Evaporation . 17 3.1.1 Introduction . 17 3.1.2 Definitions . 17 3.1.3 Determination of evaporation on the basis of the water balance equation . 18 3.1.4 Determination of evaporation on the basis of the energy balance equation and the water vapour transport . 19 3.1.5 Estimation of evaporation on the basis of data from the meteorological standard measuring network . 20 3.1.5.1 Computation procedures for evaporation from water bodies . 20 3.1.5.2 Computation procedures for potential evaporation . 21 3.1.5.3 Computation procedures for actual evaporation from areas of land . 22 3.2 Heavy rainfall point statistics . 24 3.3 Regionalization in hydrometeorology . 25 3.3.1 Introduction . 25 3.3.2 Cartographic representation of regionalized precipitation data . 27 3.3.3 Cartographic representation of regionalized heavy rainfall amounts . 27 3.3.4 Cartographic representation of regionalized extreme values of precipitation supply . 30 3.4 Probable maximum precipitation (PMP) . 30 3.4.1 General . 30 3.4.2 Estimation of PMP using a physically-based evaluation of meteorological data . 31 3.5 Snowmelt . 31 4. ESTIMATION OF AREAL PRECIPITATION AND AREAL EVAPORATION . 34 4.1 Fundamentals . 34 4.2 Methods for the computation of areal values . 34 4.3 Error sources in areal computation . 35 4.4 Computation of areal precipitation . 35 4.5 Areal evaporation . 37 5. QUANTITATIVE PRECIPITATION FORECASTING . .39 5.1 Precipitation . 39 5.2 Quantitative precipitation forecasting procedures . 40 5.2.1 Synoptic-statistical procedures . 40 5.2.2 Stochastic procedures . 42 5.2.3 Dynamic models . ..