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Water and Human Societies Spread of human population and formation of civilizations are correlated with the availability of fresh water. The Mesopotamian civilization , widely considered as the cradle of civilization, was in the the area between the and Euphrates Rivers . Contemporary distribution of human population in the United State is not an exemption. It is easy to see that the climatology of precipitation somewhat has dictated the density of human population in the US. Most of the biggest cities and economies of the country are in the vicinity of lakes, rivers and estuaries. The explained correlation clearly does not come as a surprise because water is an essential element not only for survival of human populations but it is the most critical ingredient for food production, formation of central governance, and thus fundamental to human societies. Hydrology is the study of water and its transport in all of its phases (i.e., solid, liquid, vapor) across different elements of hydrosphere , which is a region between 1 km deep in the lithosphere and 15 km high in the atmosphere. These days, hydrology is a science and largely focuses on terrestrial water cycle in continental and global scales under natural condition , without direct human control or intervention, which makes it distinct from classic hydrologic and hydraulic engineering . Figure 1: Left: U.S. population density. Right: U.S. mean annual precipitation [mm]. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 1

Water Resource Management: An Interdicsiplinary Science Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 4

Hydrologic Cycle Study of the circulation of water between the earth surface and its atmosphere, known as the hydrologic cycle , is central to hydrology. The hydrologic cycle explains flux of water across different water reservoirs . Global Water Cycle Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 7

Hydrologic Cycle - Processes and Fluxes Hydrologic cycle occurs through water fluxes across different water reservoirs. Water flux is the mass of water, per unit area and time (e.g., kg m -2 s -1 ), across the water reservoirs in the hydrosphere . The water fluxes can be in various phases such as vapor, liquid, and/or solid. A conceptual schematic of the fluxes between the Earth’s water reservoirs is shown in the following figure. EVAPORATION FROM WET VEGETATION AND PUDDLES * * * * * * * * PRECIPITATION SNOWMELT RUNOFF CLOUD FORMATION DEPRESSION STORAGE FROM FALLING RAIN OVERLAND FLOW INFILTRATION WATER TABLE (WT) SOIL MOISTURE BASE FLOW SPRING WT WT WT IMPERMEABLE LAYER (I L) GROUNDWATER STREAM FLOW LAKE OR SEA TRANSPIRATION FROM STREAMS AND OPEN WATER FROM SOIL IL INTERCEPTION Percolation Recharge Interflow Figure 7: Hydrologic water cycle and fluxes. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 10

Hydrologic Cycle - Driver II As explained, the convective motions of air and water masses in atmosphere are mainly because of an existing pressure gradient . We will discuss in the next chapter that, as a general rule, when the temperature of an air parcel increases at a constant pressure, based on the ideal gas law, its density reduces and vice versa. Therefore, in general, a cold air mass is denser than a warm air mass at constant pressure. Because the air is compressible , the density of cold air column decays faster than the density of a warm air column from earth surface to higher altitudes. Due to higher pressure of warm air column aloft than the cold air column, the air flows from warm to cold regions at high elevations (Figure 9 , left). As the air flows from warm to cold areas, the cold air column becomes heavier and its pressure increases at the surface. As a result, a surface air flow forms from cold to warm areas which eventually gives rise to a circulation pattern (Figure 9 , right). 88 hpa 840 hpa 380 hpa 850 hpa 102 hpa 860 hpa air moves from warm to cold due to pressure gradient aloft 370 hpa 835 hpa WARM AIR COLUMN COLD AIR COLUMN WARM AIR COLUMN COLD AIR COLUMN Circulation Circulation Figure 9: The circulation of the earth’s atmosphere is due to formation of a pressure gradient from warm (tropics) to cold (polar regions) air masses. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 13

Hydrologic Cycle - Driver V As a result of the Coriolis and pressure gradient forces, those large hypothetical circulation cells (Figure 10 , left) breaks into three smaller cells as shown below. As we know how the Coriolis force deflects air parcel movements, it is easy to conclude that the “surface” air flows from mid-latitudes high-pressure areas towards the tropical low-pressure convergence zones are deflected towards east. These surface air flows are called Easterlies or trade winds . On the other hand, surface air flows from high-pressure horse latitudes towards polar fronts are deflected to the west and create the Westerlies . S N W E -60 -30 +30 +60 L H L H L Westerlies Easterlies Horse Latitudes ITCZ Polar Fronts Figure 13: Schematic of a three-cell atmospheric circulation model and deflection of airflows in northern and southern hemisphere. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 16

Water Properties - Water density: ρ w = 1000 [kg m -3 ] - Ice density: ρ c = 917 [kg m -3 ] - Specific heat capacity: is the heat Q [J] required to raise the temperature T of the unit mass of a given substance by one degree of Kelvin, which is c = Q / ( m Δ T ) [Joule Kg -1 K -1 ] . Depending on the temperature 5 ◦ ≤ T ≤ 100 ◦ C , the specific heat capacity of water varies between 4180 to 4220 [Joule Kg -1 K -1 ]. Temperature (C) p [kg m-3] c (J Kg- 1 K- 1} 0.01 999.87 4 2 17 15 999.13 4186 30 995.67 4177 ' - Latent heat capacity ( L ): is the heat Q required for phase change of unit mass of a substance, that is L = Q / m . During the phase change, the temperature of the substance remains unchanged. Latent heat of vaporization: L v = 2 . 5 × 10 6 [J Kg -1 ] Latent heat of melting (fusion): L s = 3 . 34 × 10 5 [J Kg -1 ] Latent heat of sublimation: L sv = 2 . 86 × 10 6 [J Kg -1 ] and thus L sv = L s + L v Figure 17: Mean global heat budget at the earth surface in [W m -2 ], where R n is the net solar radiation at the surface, L e E is the latent heat flux and H denotes the sensible heat flux. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 19

Water Budget and Mass Balance Water budget analysis is extremely important for sustainability of water resources management. Water mass balance analysis in hydrologic systems assesses storage of water in natural or man-made reservoirs and evaluates continuity of water flow across those reservoirs. We often use a system approach to explain hydrologic processes. Mass of water parcels is considered as a conserved quantity and a simple mass balance over a system of water storage can be cast as follows: System Input Output Input Output System accumulation (Δ S ) = Input ( I ) - Output( O ) [L 3 ] . We naturally evaluate the above mass balance equation over a certain of period time Δ t as: Δ S Δ t = I Δ t - O Δ t [ L 3 T - 1 ] Thus, we have Δ s Δ t = Q in - Q out [ L 3 T -1 ] . In a steady state condition the mass balance reduces to Q in = Q out as Δ s Δ t = 0. Note that we often express hydrologic flows/fluxes per unit area such as [m 3 m -2 s -1 ]= [m s -1 ] or [mm hr -1 ] or [mm day -1 ] , which is common for representation of the precipitation or evapotranspiration fluxes. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 20

Reservoir Water Budget Review of some important units: - Length: 1 [inch] = 2.54 [cm], 12 [inches] = 1 [ft] - Area: 1 [acre]= 1 640 [miles 2 ] = 43,560 [ft 2 ] = 4,047 [m 2 ] - Volume: [ac.ft] = 43,560 [ft 3 ] = 1233.5 [m 3 ] - Discharge: [m 3 s -1 ] or [cfs], where 100 [cfs] = 2.83 [m 3 s -1 ] P A + Q in + G in - E A - Q out - G out = Δ S Δ t [L 3 T - 1 ] (1) P + Q in A + G in A - E - Q out A - G out A = Δ S A Δ t [L T - 1 ] (2) Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 21

Watershed Water Budget One crucial step in hydrologic mass balance analysis is defining the boundary or control volume of the system such as a small pond, a large dam or a watershed . A watershed is defined as a locus of all points (pixels of a digital elevation model) on the earth’s surface that drain precipitation water to a single point, called the watershed outlet . The boundary of a watershed is called the divide . Watersheds can be delineated either manually or automatically using digital elevation models (DEM) and computational algorithms. The size of a watershed can range from a few acres to millions of square miles (Amazon River Basin) – depending on the geomorphologic characteristics of land surfaces and location of the outlet. Figure 18: A schematic of a watershed and its divide (left). A schematic of how watersheds are nested (right, credit: Marsh, 1998, p. 170) Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 22

Watershed Water Budget On a global scale , as earth is a close thermodynamic system, water mass balance at the earth’s surface is dS dt = P - ET . In a steady state condition this mass balance leads to P = ET . The steady state assumption is a function of the time-scale . The global steady state assumption is valid for sufficiently long period of time such as a year, because evapotranspiration and precipitation are highly dynamic processes that vary significantly in a shorter time scale. However, based on the law of conservation of mass it is easy to conclude that on an annual basis the steady state assumption is reasonable and precipitation and ET are equal. As the time scale increases the accuracy of this mass balance also increase. Observational evidence suggests that the annual rate of both precipitation and ET is approximately 1000 [mm yr - 1 ] . At a watershed scale , each basin may exchange water mass with its surrounding basins through the underlying groundwater systems. A watershed mass balance can be written as follows: dS Adt = P + G in A - ET + Q A + G out A [L T - 1 ] . After averaging over sufficiently long period of time, for a steady state condition , we have P + G in / A = ET + Q / A + G out / A . Long resident time of groundwater implies G in ≈ G out → 0: P ≈ Q / A + ET ⇒ ET ≈ P - Q / A . When a storm is occurring, the air humidity is relatively high, which reduces the ET significantly. Assuming (ET ≈ 0), the watershed mass balance can be reduced to P ≈ Q / A . Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 23

Hydrologic Cycle and Satellites Remote sensing has provided new insights for deeper understanding of hydrologic cycle in the past few decades. Satellites , including those launched by NASA, have provided invaluable information about global land and sea surface temperatures (e.g., Advanced Very High Resolution Radiometer, AVHRR ), atmospheric moisture (e.g., Atmospheric Infrared Sounder, AIRS ), precipitation (e.g., Global Precipitation Measuring, GPM), snow (e.g., Special Sensor Microwave Imager/Sounder, SSMI/S ), soil moisture (e.g., Soil Moisture Active Passive satellite, SMAP ), vegetation coverage (e.g., Moderate-Resolution Imaging Spectroradiometer, MODIS ), and even changes in ground water elevation (e.g., Gravity Recovery and Climate Experiment, GRACE ). Figure 19: NASA Earth Science Division Operating Missions – 2019. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 24

Hydrologic Hazards Floods: Flood prediction and management is an important topic in hydrologic engineering. A flood is an overflow of water that submerges land surfaces that are usually dry. Flooding may occur as an overflow of water from water bodies, such as rivers, lakes, or oceans. Figure 20: These images on 17 May and 24 October 2013, show the impact of Typhoon Nari and heavy seasonal rainfall on Cambodia’s Mekong and Tonle Sap Rivers. More than half a million people were affected by the flood and more than 300,000 hectares of rice fields were destroyed. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 25

Floods in U.S. o California Flooding - February 2017: Heavy, persistent rainfall across northern and central California created substantial property and infrastructure damage from flooding, landslides and erosion. Notable impacts include severe damage to the Oroville Dam spillway, which caused a multi-day evacuation of 188,000 residents downstream. Excessive rainfall also caused flood damage in the city of San Jose, as Coyote Creek overflowed its banks and inundated neighborhoods forcing 14,000 residents to evacuate. Total Estimated Costs: $ 1.5 Billion; 5 Deaths o Louisiana Flooding - August 2016: A historic flood devastated a large area of southern Louisiana resulting from 20 to 30 inches of rainfall over several days. Watson, Louisiana received an astounding 31.39 inches of rain from the storm. Two-day rainfall totals in the hardest hit areas have a 0.2% chance of occurring in any given year: a 1 in 500 year event. More than 30,000 people were rescued from the floodwaters that damaged or destroyed over 50,000 homes, 100,000 vehicles and 20,000 businesses. This is the most damaging U.S. flood event since Superstorm Sandy impacted the Northeast in 2012. Total Estimated Costs: $ 10.0 ( $ 10.3) Billion; 13 Deaths o Texas and Oklahoma Flooding and Severe Weather - May 2015: A slow-moving system caused tremendous rainfall and subsequent flooding to occur in Texas and Oklahoma. The Blanco river in Texas swelled from 5 feet to a crest of more than 40 feet over several hours causing considerable property damage and loss of life. The city of Houston also experienced flooding which resulted in hundreds of high-water rescues. The damage in Texas alone exceeded 1.0 (1.1) billion. There was also damage in other states (KS, CO, AR, OH, LA, GA, SC) from associated severe storms. Total Estimated Costs: $ 2.5 ( $ 2.6) Billion; 31 Deaths o Northern Plains Flooding - Spring 1997: Severe flooding in North Dakota, South Dakota and Minnesota due to heavy spring snow melt. This flooding caused widespread damage to agriculture, infrastructure, homes and businesses. Total Estimated Costs: $ 3.7 ( $ 5.7) Billion; 11 Deaths source: https://www.ncdc.noaa.gov/billions/events.pdf Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 26

Hydrologic Hazards Droughts: Droughts continue to be one of the most severe weather-related problems in the world. Figure 21: California Drought: left image is on Jan 2014 and right image is on Jan 2017 Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 27

Hydrologic Hazards Droughts: Droughts continue to be one of the most severe weather-related problem around the world. - Meteorological droughts – lack of precipitation - Agricultural droughts – lack of soil moisture - Hydrological droughts – reduced stream flow and groundwater levels Figure 22: California Drought in 2014—a closer look. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 28

Droughts in U.S. o Western Drought - 2014: Historic drought conditions affected the majority of California for all of 2014 making it the worst drought on record for the state. Surrounding states and parts of Texas, Oklahoma and Kansas also experienced continued severe drought conditions. This is a continuation of drought conditions that have persisted for several years. Total Estimated Costs: $ 4.0 ( $ 4.2) Billion; 0 Deaths o U.S. Drought/Heatwave - 2012: The 2012 drought is the most extensive drought to affect the U.S. since the 1930s. Moderate to extreme drought conditions affected more than half the country for a majority of 2012. The following states were affected: CA, NV, ID, MT, WY, UT, CO, AZ, NM, TX, ND, SD, NE, KS, OK, AR, MO, IA, MN, IL, IN, GA. Costly drought impacts occurred across the central agriculture states resulting in widespread harvest failure for corn, sorghum and soybean crops, among others. The associated summer heatwave also caused 123 direct deaths, but an estimate of the excess mortality due to heat stress is still unknown. Total Estimated Costs: $ 30.0 ( $ 32.4) Billion; 123 Deaths o Southern Plains/Southwest Drought & Heat Wave - Spring-Summer 2011: Drought and heat wave conditions created major impacts across Texas, Oklahoma, New Mexico, Arizona, southern Kansas, and western Louisiana. In Texas and Oklahoma, a majority of range and pastures were classified in ”very poor” condition for much of the 2011 crop growing season. Total Estimated Costs: $ 12.0 ( $ 13.3) Billion; 95 Deaths source: https://www.ncdc.noaa.gov/billions/events.pdf http://droughtmonitor.unl.edu/MapsAndData/MapArchive.aspx Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 29

Hydrologic Sustainability Sustainable development is the development that can meet the needs for the present generation without compromising the ability of future generation to meet their own needs. Hydrologic sustainability refers to engineering and management practices that enable us and ecosystem to have access to water in sufficient quantity and quality at present without compromising the ability of future generation to meet their own needs to freshwater resources. Challenges to sustainability: Urbanization: By 2050 more than 9 billion people will live on the Earth. Now we have more than 22 cities with more than 10 million inhabitants. The challenges are related to water supply, drainage, waste and storm water collection and treatment. The excessive demand exerts immense pressure on our natural water resources systems. Climate Change: A change in the state of climate that can be identified by changes in the mean and/or variability of its properties that can persist for an extended period of time – typically decades or longer (IPCC). The climate system consists of five major components: the atmosphere, the hydrosphere, the cryosphere, the land surface, and the biosphere. These subsystems are influenced largely by the human activity and extraterrestrial sources such as the Sun. https: //www.esrl.noaa.gov/gmd/ccgg/trends/full.html Sustainability of hydrologic systems can be quantified in terms of their water mass balance. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 30

Lack of the Hydrologic Mass Balance Lake Urmia is a prime example of a water body with an imbalanced water budget. The Urmia lake, once was the sixth largest saltwater lake on earth has shrunk to 10% of its original size in recent decade, mainly due to damming (less inflow) and excessive groundwater withdrawals (more outflow) for agricultural water use. The following animation shows shrinkage of the lake surface from 1984-2014. We can see that how a simple mass balance problem can have significant unforeseen ramifications for regional ecology and human population. Figure 23: Lake Urmia (area: 5200 km 2 ) in north west of Iran has been shrinking in the past decades from 1998 (left) to 2011 (right) due unsustainable regional water resource management (credit: NASA). Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 31

Lack of the Hydrologic Mass Balance Formerly one of the four largest lakes in the world with an area of 68,000 km2 (26,300 sq mi), the Aral Sea has been steadily shrinking since the 1960s after the rivers that fed it were diverted by Soviet irrigation projects. By 1997, it had declined to 10% of its original size. Figure 24: Shrinkage of the Aral Sean from 1960 to 2014. Hydrology and Design–CEGE 4501, Chapter 1: Hydrologic Cycle and Mass Balance Ardeshir Ebtehaj 32