Weather Modification and its Hydrologic Impact on the North Platte Watershed, Wyoming

The longer droughts in the arid regions caused the necessity of weather modification (WM), or cloud seeding programs, to increase precipitation and end drought by utilizing the clouds in the sky. Stream flow changes due to cloud seeding operations in the North Platte Watershed, Wyoming, are quantified for various temperature and land use conditions. The variable infiltration capacity (VIC) land surface hydrological model is calibrated and validated for the periods of 1950-80 and 1980-2000 respectively, using daily meteorological forcing and stream flow data. Model simulations are carried out for various scenarios and; simulated stream flow is compared with historical stream flow. The annual stream flow shows a maximum decline of about 3.5% for a temperature rise of 1.5 degree Celsius. The wet months are getting wetter and dry months are further drying, with increase of temperature for future climate. The model simulates more than 15% increase of annual stream flow in the watershed, when simulated under a temperature rise of 1.5 degree Celsius and an anticipated increase (10%) of precipitation from cloud seeding operations. But this increase of annual stream flow is not fully sufficient to reduce the impacts of declining stream flow during summer periods. Simulations are also performed to identify the most favorable land-use and effective region for cloud seeding inside the watershed. The central-west and south-west regions of the watershed, which consist of higher percent coverage of evergreen needle leaf forest, are found more effective for cloud seeding operations. The north-west region, with higher coverage of open shrub lands and grass lands, shows minimum effectiveness for these operations.