Design of meteorological data networks Dr. Anil Kumar Lohani National Institute of Hydrology, Roorkee India Hydro-Met Network Design Workshop, April 6-11, 2015 Kolkata

OBJECTIVES OF NETWORK DESIGN  Water resources assessment at basin or sub-basin scale  Water resources assessment for administrative geographical unit  Water resources project planning including:  Irrigation,  Domestic (domestic use, livestock watering),  Hydroelectric power and other power generation,  Environmental requirements,  Industrial requirements,  Navigation,  Tourism, recreation  Flood management  Assessing impacts of Climate Change on Water Resources

Why hydrometeorologic networks? 3 An appropriate hydro-met network provide the desired information

Questions pertaining to the collection of hydrological data What hydrological variables need to be observed? Where do they need to be observed?How often do they need to be observed? What is the duration of the observation programme? How accurate should the observations be?

Monitoring Networks A monitoring network is composed of a group of observational stations, set-up and operated to observe underlying variables and address a single or a set of interrelated objectives. Average area served by a hydrological station is known as density of a hydrological network. 5

Minimum Network Minimum number of stations necessary to initiate planning for the economic development of the water resources Minimum network will avoid serious deficiencies in developing and managing water resources on a scale commensurate with the overall level of economic development of the country Developed as rapidly as possible by incorporating existing stations as appropriate May not be adequate for the formulation of detailed development plans

Conducting network analysis

Determine cost of establishing and running network: costs for land acquisition, station construction, equipment, operation, maintenance, staff costs, etc. An optimum network is obtained when amount and quality of data collected is economically justifiable and meets users’ needs. Network should be evaluated/ reviewed periodically. Design of Monitoring Networks

TYPES OF NETWORKS BASIC OR PRIMARY NETWORK: Provide basic/minimum data for studies and should run continuously and indefinitely. Low density of stations. SECONDARY NETWORK: are operational for a short time to establish a good correlation with principal stations. Density supplementary to basic network, to meet accuracy demands. DEDICATED NETWORK put in place for a certain project: project objectives determine network density and period of operation. NETWORKS FOR REPRESENTATIVE BASINS: to study certain phenomena in detail, e.g., for research purpose.

Network review and design Institutional set-up: to ensure co-ordination/integration of data collection networks. 2.Data need identification: existing and potential future data users are approached to identify their data needs. 3.Objectives of network: based on outcome of step 2, objectives of required network are determined. 4.Prioritisation: a priority ranking among objectives is made in case of budget constraints. 5.Network density: based on objectives, required network density is determined, taking in view correlation structure of variable(s).

6.Review existing network: existing network density versus required, available equipment and its adequacy, adequacy of operational procedures and possible improvements. 7.Sites and equipment selection: if existing network requires expansion. 8.Cost estimation: costs to construct, operate and maintain existing and new stations. 9.Cost-effectiveness analysis: cost and effectiveness are compared. Steps 5 to 8 are repeated if budget is insufficient to cover costs. 10.Implementation: once design is approved, network is implemented. 11.Network should be reviewed after 3 to 5 years. Above procedure should be repeated. Steps for network review and design....

RAINFALL NETWORK: Measuring Objective  Water resources assessment, projects planning and management  Drinking/ Industrial/ Municipal water supply, Navigation, Recreation Activities  Hydrologic design of structures,  Agriculture Water Management  Irrigation, Rain-fed agriculture  Disaster warning systems, and protection:  Flooding, Drainage, Hydrological forecasting  Ecologically sound water systems:  Ecology and Forestry, Erosion, Discharge of effluents  Hydropower generation  Research Major uses of Rainfall data

 Ultimate aim from RF network is to get reliable estimates of areal RF, and/or long term mean values.  Due to spatial correlation among point RF stations and (near) absence of serial correlation, these objectives will lead to different networks.  Correlation reduces effective number of data.  Due to spatial correlation, data in time are more effective then data in space.  A less dense network operated for a longer period is more cost-effective than a denser network providing the same number of RF data.  A reduction in network density adversely affects quality of individual areal estimates. RAINFALL NETWORKS

Network Design: Measure of Effectiveness  To evaluate an optimal design of monitoring system, a measure is required to quantify its effectiveness.  This measure depends on monitoring objectives and should be related to admissible error in estimating the underlying variable.  This error is a function of sampling locations, frequency and accuracy.

Methods of Network Design 1.C v Method 2.Key Station Network Method 3.Spatial correlation Method 4.Entropy Method 5.WMO Guidelines

NETWORK DENSITY WMO recommendations (2008) for minimum densities of stations (area in km 2 per station)

WMO (2008) recommended minimum densities of river gauging stations (area in km 2 per station) NETWORK DENSITY Physiographic unit StreamflowSedimentsWater quality Coastal Mountains Interior plains Hilly/undulating Small islands Urban areas--- Polar/arid

Prioritisation system l In the first instance, “ideal” network size is determined. l All potential users of data should be consulted. l Each station in “ideal” network should be prioritised. NETWORK DENSITY

Classification of c

CWC Network

IMD AWS Network

IMD – DRMS Network

ISRO Network

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