Dr. Nicolas Zegre Understanding the Hydrologic Cycle

Global Water Resources Oceans = 96.5% of all water on Earth 0.001% in the atmosphere Freshwater = 2.5% of total global storage 69.56% is in icecaps, glaciers, & frozen water 30.1% is groundwater & 0.05% is soil moisture Leaving 0.29% surface water (0.008% of all water on Earth!) Dingman Table 3-1 Oceans96.5% Fresh water 2.5% Ice & snow 69.56% Liquid water 30.44% Ground water 98.8% Soil moisture 0.2% Streams, lakes 1% All waterFresh waterLiquid fresh water

Water as a scarce resource Human constraints Population growth Urbanization Industry and agriculture Wasteful practices Conflicts Between human uses Between different groups of humans Between humans and ecosystems “ There is no shortage of water in the desert but exactly the right amount…There is no lack of water here, unless you try to establish a city where no city should be.” Edward Abbey, Desert Solitaire Laituri, CSU

Where we are headed… qualitative and quantitative understanding of concepts and physical principles that govern occurrence, distribution, and circulation of water emphasis on physical understanding and parameterization of hydrologic processes - how does rainfall become streamflow? - how long does water stay in a watershed?

Overview Hydrologic Cycle

To understand hydrological processes, we need to focus on a manageable control volume: the catchment or watershed

Why the watershed? Known inputs Known boundaries Integrates multiple systems e.g. biochemical, ecological, hydrological Eagleson, 1991

Space-time scales Local scale Hillslope/field scale Headwater/ catchment scale River basin scale Continental scale Brutsaert, 2005

Stream Order Streams within watersheds are often classified hierarchically Segments categorized by their order in the system Horton – Strahler method About 85% of all stream miles in the U.S. are first to third order streams … close to 3 million miles

Hydrologic Cycle Hendriks 2010

The Hydrologic Cycle From Ross Woods AtmosphereContinent

Hydrologic Continuity Equation General terms: Rate of accumulation of mass or volume in system = Input rate - output rate Hydrologists (density ~ constant w/ T, thus use V): Assumptions: We can measure or estimate all of the components Storage

Water Balance Components Et

Residence time Atmospheric water Surface water Ocean water Groundwater Residence time, T r : measure of the average time a molecule of water spends in a reservoir Average residence times 4 y 20,000 y 2,650 y 0.02 y

Controls on the Hydrologic Cycle

Climate, Morphology, & Landcover Controls on hydrology Jones et al, 2012 WATER-LIMITED ENERGY-LIMITED

Controls on hydrology Climate, Morphology, & Landcover Including topography, organization, soils & geology McGuire et al., 2005 WRR

Controls on hydrology Climate, Morphology, & Landcover Including topography, organization, soils & geology

Climate, Morphology, & Landcover Controls on hydrology

Flow Paths to the Stream saturation excess infiltration excess Surface flow – rapid delivery of water to stream

Subsurface flow – slower delivery of water to stream Flow Paths to the Stream

Importance of existing moisture in watershed (pre-event water) Flow Paths to the Stream

Basin Stores & Processes Hendriks 2010 Input or output processes Storage Lowercase = hydrologic processes