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WEATHER Why study weather? ACWADAM Plot no.4, Lenyadri CoCo-op Hsg. Society, Sus Road, Pashan Pune Phone:020--25871539 Phone:020 Email: [email protected] Why study Weather? Affects Nature as well as lives and livelihoods natural disasters like floods Droughts Cyclones Storms Landslides Weather is one of the fundamental process that shapes the earth – Weathering – Erosion Human activities like industries cause adverse effect on climate – Acid rain due to excessive SO2 and NO. – Air pollution due to CO2 emitted from vehicles In the past human settlements have been affected by the change in climatic conditions – Desertification of Middle East Lives and livelihood Heat wave (More than average temp.) Cold wave (Less than average temp.) Affects farmers the most ….. Damage to crops due to; Delayed rainfall Excessive rainfall Untimely rainfall No rainfall Affects the cattle and other livestock Thus affects the total economy of the country In India: Diversity in weather conditions or weather types More than 70% people are engaged in agriculture with almost 80% of them depending on rain. Weather data is necessary for any kind of planning of watershed program For the study of water balances…. balances…. …And for the sustainable development and management of the program Lack of scientific knowledge and data for analysis Need to understand Weather for a total implementation of a watershed project as weather plays a key role in the entire program India: Rainfall –Annual and Monsoon season Source: Indian Meteorological dept. Weather science The science of studying weather is called as Meteorology-Meteorology – where some predictions can be made using atmospheric conditions. – Or some data can be generated using simple equipments. – Which in turn can be used for better implementation of a watershed project Measurement of weather parameters like evaporation help in many ways for better understanding of the area Weather Weather is the specific condition of the atmosphere at a particular place and time. It is measured in terms of wind wind,, temperature temperature,, humidity,, atmospheric pressure, humidity pressure, cloudiness cloudiness,, and precipitation precipitation.. In most places, weather can change from hourhour-totohour, dayday-toto-day, and seasonseason-toto-season. The average weather over a longer period is known as the climate climate.. What causes weather? Changes in weather occur due to the movement of air, driven by – the heat energy from the sun; – the rotation of the Earth. Together these forces drive the atmosphere to circulate on a global scale. scale. The local temperature, pressure, moisture content, precipitation, cloud cover, and wind describe the air mass, and together these make up the weather. Satellite image indicates: Temperature, cloud cover, Sea surface temperature over the world. Weather factors Global scale Regional scale Some other factors influencing weather are: Geographic location: location: whether it is in the tropics, equator or temperate region Surface features and terrain: terrain: Whether it is an island or peninsular region, hilly area or plains Altitude:: whether it is closer to sea or it is located at a Altitude high elevation Parameters Basically when we speak of weather we speak about: atmosphere, Rainfall/precipitation cloudiness, wind speed & wind direction Other factors we consider during watershed management are: Atmospheric pressure Humidity Solar radiation Evaporation Evapotranspiration Atmosphere It is a mixture of gases. Transfer of energy takes place in the atmospere Protects earth from harmful solar radiation Comprises of four layers Troposphere, Stratosphere, Mesosphere and Thermosphere Clouds Low Level cloud Medium Level cloud High level cloud A cloud is a collection of minute particles of water or ice suspended in the air. air. Important for energy balance of the earth. Important for water transport Instrumental in determining climatic zones of the earth Classified into low level, medium level and high level clouds Wind and solar radiation Wind Wind is simply air in motion. Generally flows over the surface of earth from high pressure to low pressure. pressure. Winds are determined by the direction from which they blow e.g. easterlies/ westerly. The two commonly measured parameters used to measure wind are: direction and speed. Solar radiation Solar radiation is the intensity of the sun’s rays reaching the surface of the earth. More the solar radiation more will be the losses of water vapour from the surface. Atmospheric pressure and humidity Atmospheric pressure Humidity Pressure on a point on the ground, is the weight of the column of air above that point. point. Depends upon the altitude. Sea level -more pressure than mountain peak Never constant and keep changing depending upon convergence or divergence of air on global scale. Generally, some measure of the water vapour content of the air. At different temperatures the air contain different amounts of water vapour Warm air can hold more water vapour than cold air. Generally measured in the form of relative humidity in percentage (water vapour in a column of air) Evaporation and Evapotranspiration Evaporation It is the process by which water becomes vapour suspended in air molecule. It is directly proportional to temperature and wind speed and inversely proportional to the humidity. Evapotranspiration Evapotranspiration is a measurement of the amount of water vapor returned to the air in a given area. The losses are by: – evaporation and – transpiration (active exhalation of water through plant skin) Opposite of rainfall Rainfall/Precipitation Any liquid or solid form of water particles that falls from the atmosphere and reaches the Earth's surface is known as precipitation. Precipitation can occur in a variety of forms such as drizzle, hail, rain, sleet or snow. snow. Rainfall processes Orographic rainfall: rainfall: Due to effect of altitude. Convection: Most Convection: common process Cyclonic wedging: wedging: When two air fronts meet this type of rain occurs. Heavy rainfall for about 77-8 hours Easily measurable units on field: Evaporation Rainfall Hydrological cycle In a hydrological cycle, Inflow and Outflow of water is very important. Inflow is by means of Rain, hail, dew or snow. snow. Outflow is by means of evaporation and transpiration.. transpiration Other weather factors add to or reduce the rate of evaporation. Therefore measurement of weather parameters are necessary in the study of hydrological cycle and eventually watershed management. Measurement of rainfall gives a clear idea about excess or deficit of rainfall-- Useful for rainfall calculating 1.Surface runoff 2.Infiltration 3.Recharge;; 3.Recharge and also for planning the next crop using soil moisture content as an indicator. In a watershed, I=O+ losses; losses; where I in inflow and O is outflow . To get the balance, correct knowledge of total rainfall received over certain area is important. Rainfall is measured using rain gauges and is expressed in mm or inches of rainfall over the area. Rainfall can be measured on field using simple rain gauges The losses in water cycle occures in many ways. 1. Absorbed by the soil through infiltration 2. Flow as surface flow or runoff 3. Water held in soil or surface gets evaporated or is transpired by vegetation. This loss can be measured in meteorology using instruments like evaporimeters The evaporation is measured in mm/day Evaporation can also be measured using empirical formulae where other factors like wind speed, humidity, solar radiation and pressure are taken into consideration. Impacts on livelihood Different areas with different weather conditions (Micro climate) Weather conditions differ within 10 km. Example: Kolwan valley Area 80 sq/km E-W distance 12km. Rain gauges installed at 8 villages Karmoli Average rainfall at Karmoli: 1400mm Average rainfall at Chikhalgaon: 1800mm. Average rainfall at Hadashi: 2200mm Average evaporation at Bhalgudi: 7-7.6mm/day Average evaporation at Chale: 6-6.5mm/day Average evaporation at Chikhalgaon: 6.2-6.8mm/day Though weather conditions remain constant over the period, there is a great variability within the area. Two examples in Pune district illustrated bellow: bellow: Kolwan valley Distance from Pune:40 km Geology: Deccan basalt Soil type: Red to reddish brown silty soils and black clayey soils (alfisols &vertisols) Average rainfall: 1800mm Climate: semiarid Crops: Rice, sugarcane & wheat Area covered under DPAP Purandhar Distance from Pune:60 km Geology: Deccan basalt Soil type: Red to reddish brown silty soils and black clayey soils (alfisols &vertisols) Average rainfall: 500mm Climate: semiarid Crops: Jowar, ground nut and orchards Area covered under DPAP Watershed approach may be different for the two areas Kolwan valley More rainfall therefore more runoff… need to impound runoff. Structures may be constructed in such a way that it should sustain at high intensity rainfall conditions. Alternative source for water like springs can be considered Purandhar Less rainfall therefore all water needs to be harvested using trenches etc. Limited structures could be constructed considering recharge and discharge areas. Proper water management should be done involving community participation Different methods of water management required for different areas Breaching of earthen check dam due to heavy rainfall Adequate water storage through earthen check dam in Purandhar Impact assessment As the difference is so significant within such a small distances, there is a great need to have accurate data for a specific area of interest. At government level, rainfall and evaporation data is available at taluka HQ which may not represent the actual value at the field. Therefore such data if generated locally, may prove useful for watershed planning and development of the area. As solution to different areas may be different and same parameters can not be applied everywhere. In watershed management program weather data can be used for: Construction of structures; Deciding upon crop to be grown in the area; Implementation of other watershed techniques like contour trenching, bunds etc; Calculating water budget for accurate management of water available resources; Future planning of other schemes Preparation of data base for future generation for reference or academic purposes. Thank you for your attention