Geology topics

Kiyomi Morino

Publications and source records attributed to Kiyomi Morino.

7 recordsLinked to original sources

USGS2016

Increasing influence of air temperature on upper Colorado River streamflow

This empirical study examines the influence of precipitation, temperature, and antecedent soil moisture on upper Colorado River basin (UCRB) water year streamflow over the past century. While cool season precipitation explains most of the variability in annual flows, temperature appears to be highly influential under certain conditions, with the role of antecedent fall soil moisture less clear. In both wet and dry years, when flow is substantially different than expected given precipitation, these factors can modulate the dominant precipitation influence on streamflow. Different combinations of temperature, precipitation, and soil moisture can result in flow deficits of similar magnitude, but recent droughts have been amplified by warmer temperatures that exacerbate the effects of relatively modest precipitation deficits. Since 1988, a marked increase in the frequency of warm years with lower flows than expected, given precipitation, suggests continued warming temperatures will be an increasingly important influence in reducing future UCRB water supplies.

Geophysical Research Letters↗

USGS2014

Understanding uncertainties in future Colorado River streamflow

The Colorado River is the primary water source for more than 30 million people in the United States and Mexico. Recent studies that project streamf low changes in the Colorado River all project annual declines, but the magnitude of the projected decreases range from less than 10% to 45% by the mid-twenty-first century. To understand these differences, we address the questions the management community has raised: Why is there such a wide range of projections of impacts of future climate change on Colorado River streamflow, and how should this uncertainty be interpreted? We identify four major sources of disparities among studies that arise from both methodological and model differences. In order of importance, these are differences in 1) the global climate models (GCMs) and emission scenarios used; 2) the ability of land surface and atmospheric models to simulate properly the high-elevation runoff source areas; 3) the sensitivities of land surface hydrology models to precipitation and temperature changes; and 4) the methods used to statistically downscale GCM scenarios. In accounting for these differences, there is substantial evidence across studies that future Colorado River streamflow will be reduced under the current trajectories of anthropogenic greenhouse gas emissions because of a combination of strong temperature-induced runoff curtailment and reduced annual precipitation. Reconstructions of preinstrumental streamflows provide additional insights; the greatest risk to Colorado River streamf lows is a multidecadal drought, like that observed in paleoreconstructions, exacerbated by a steady reduction in flows due to climate change. This could result in decades of sustained streamflows much lower than have been observed in the ~100 years of instrumental record.

Colorado River↗

USGS2013

Phreatophytes under stress: transpiration and stomatal conductance of saltcedar ( Tamarix spp.) in a high-salinity environment

Background and aims: We sought to understand the environmental constraints on an arid-zone riparian phreatophtye, saltcedar (Tamarix ramosissima and related species and hybrids), growing over a brackish aquifer along the Colorado River in the western U.S. Depth to groundwater, meteorological factors, salinity and soil hydraulic properties were compared at stress and non-stressed sites that differed in salinity of the aquifer, soil properties and water use characteristics, to identify the factors depressing water use at the stress site. Methods: Saltcedar leaf-level transpiration (EL), LAI, and stomatal conductance (GS) were measured over a growing season (June–September) with Granier and stem heat balance sensors and were compared to those for saltcedar at the non-stress site determined in a previous study. Transpiration on a ground-area basis (EG) was calculated as EL × LAI. Environmental factors were regressed against hourly and daily EL and GS at each site to determine the main factors controlling water use at each site. Results: At the stress site, mean EG over the summer was only 30 % of potential evapotranspiration (ETo). GS and EG peaked between 8 and 9 am then decreased over the daylight hours. Daytime GS was negatively correlated with vapor pressure deficit (VPD) (P < 0.05). By contrast, EG at the non-stress site tracked the daily radiation curve, was positively correlated with VPD and was nearly equal to ETo on a daily basis. Depth to groundwater increased over the growing season at both sites and resulted in decreasing EG but could not explain the difference between sites. Both sites had high soil moisture levels throughout the vadose zone with high calculated unsaturated conductivity. However, salinity in the aquifer and vadose zone was three times higher at the stress site than at the non-stress site and could explain differences in plant EG and GS. Conclusions: Salts accumulated in the vadose zone at both sites so usable water was confined to the saturated capillary fringe above the aquifer. Existence of a saline aquifer imposes several types of constraints on phreatophyte EG, which need to be considered in models of plant water uptake. The heterogeneous nature of saltcedar EG over river terraces introduces potential errors into estimates of ET by wide-area methods.

Colorado River↗

USGS2009

An empirical algorithm for estimating agricultural and riparian evapotranspiration using MODIS Enhanced Vegetation Index and ground measurements of ET. I. Description of method

We used the Enhanced Vegetation Index (EVI) from MODIS to scale evapotranspiration (ET actual ) over agricultural and riparian areas along the Lower Colorado River in the southwestern US. Ground measurements of ET actual by alfalfa, saltcedar, cottonwood and arrowweed were expressed as fraction of potential (reference crop) ET o (ET o F) then regressed against EVI scaled between bare soil (0) and full vegetation cover (1.0) (EVI*). EVI* values were calculated based on maximum and minimum EVI values from a large set of riparian values in a previous study. A satisfactory relationship was found between crop and riparian plant ET o F and EVI*, with an error or uncertainty of about 20% in the mean estimate (mean ET actual = 6.2 mm d −1 , RMSE = 1.2 mm d −1 ). The equation for ET actual was: ET actual = 1.22 × ET o-BC × EVI*, where ET o-BC is the Blaney Criddle formula for ET o . This single algorithm applies to all the vegetation types in the study, and offers an alternative to ET actual estimates that use crop coefficients set by expert opinion, by using an algorithm based on the actual state of the canopy as determined by time-series satellite images.

Remote Sensing↗

USGS2009

An empirical algorithm for estimating agricultural and riparian evapotranspiration using MODIS Enhanced Vegetation Index and ground measurements of ET. II. Application to the lower Colorado River, U.S.

Large quantities of water are consumed by irrigated crops and riparian vegetation in western U.S. irrigation districts. Remote sensing methods for estimating evaporative water losses by soil and vegetation (evapotranspiration, ET) over wide river stretches are needed to allocate water for agricultural and environmental needs. We used the Enhanced Vegetation Index (EVI) from MODIS sensors on the Terra satellite to scale ET over agricultural and riparian areas along the Lower Colorado River in the southwestern U.S., using a linear regression equation between ET of riparian plants and alfalfa measured on the ground, and meteorological and remote sensing data, with an error or uncertainty of about 20%. The algorithm was applied to irrigation districts and riparian areas from Lake Mead to the U.S./Mexico border. The results for agricultural crops were similar to results produced by crop coefficients developed for the irrigation districts along the river. However, riparian ET was only half as great as crop coefficient estimates set by expert opinion, equal to about 40% of reference crop evapotranspiration. Based on reported acreages in 2007, agricultural crops (146,473 ha) consumed 2.2 × 10 9 m 3 yr −1 of water. All riparian shrubs and trees (47,014 ha) consumed 3.8 × 10 8 m 3 yr −1 , of which saltcedar, the dominant riparian shrub (25,044 ha), consumed 1.8 × 10 8 m 3 yr −1 , about 1% of the annual flow of the river. This method could supplement existing protocols for estimating ET by providing an estimate based on the actual state of the canopy as determined by frequent-return satellite data.

Arizona, California, Nevada↗

USGS2008

Wide-area estimates of saltcedar (Tamarix spp.) evapotranspiration on the lower Colorado River measured by heat balance and remote sensing methods

In many places along the lower Colorado River, saltcedar ( Tamarix spp) has replaced the native shrubs and trees, including arrowweed, mesquite, cottonwood and willows. Some have advocated that by removing saltcedar, we could save water and create environments more favourable to these native species. To test these assumptions we compared sap flux measurements of water used by native species in contrast to saltcedar, and compared soil salinity, ground water depth and soil moisture across a gradient of 200–1500 m from the river's edge on a floodplain terrace at Cibola National Wildlife Refuge (CNWR). We found that the fraction of land covered ( f c ) with vegetation in 2005–2007 was similar to that occupied by native vegetation in 1938 using satellite-derived estimates and reprocessed aerial photographs scaled to comparable spatial resolutions (3–4 m). We converted f c to estimates of leaf area index (LAI) through point sampling and destructive analyses ( r 2 = 0·82). Saltcedar LAI averaged 2·54 with an f c of 0·80, and reached a maximum of 3·7 with an f c of 0·95. The ranges in f c and LAI are similar to those reported for native vegetation elsewhere and from the 1938 photographs over the study site. On-site measurements of water use and soil and aquifer properties confirmed that although saltcedar grows in areas where salinity has increased much better than native shrubs and trees, rates of transpiration are similar. Annual water use over CNWR was about 1·15 m year −1 .

Arizona, California↗

USGS2008

Scaling sap flux measurements of grazed and ungrazed shrub communities with fine and coarse-resolution remote sensing

We measured transpiration by black greasewood ( Sarcobatus vermiculatus ) (SAVE) and fourwing saltbush ( Atriplex canescens ) (ATCA) over a nitrate-contaminated aquifer in Monument Valley, Arizona, on the Colorado Plateau. Heat balance sap flow sensors were used to measure transpiration by shrubs in 2006 and 2007 and results were scaled to larger landscape units and longer time scales using leaf area index (LAI), fractional vegetation cover, meteorological data, and the enhanced vegetation index (EVI) from MODIS sensors on the Terra satellite. Transpiration was high depending on leaf area (2·95–6·72 kg m −2 d −1 ) and was controlled by vapour pressure deficit ( D ) in the atmosphere. SAVE tended to have higher transpiration rates than ATCA and had a steeper response to D , but both exhibited midday depression of leaf conductance. Over most of the site, fractional vegetation cover ( f c ) and area-wide LAI were low (0·10 and 0·37, respectively) due to heavy grazing by cattle and sheep. However, a portion of the plume that had been protected from grazing for 10 years had f c = 0·75, LAI = 2·88. Transpiration rates on a ground-area basis varied with LAI, with midsummer daily values ranging from 1·44 mm d −1 (LAI = 0·36) to 13·1 mm d −1 (LAI = 2·88 mm) over the site, corresponding to projected annual values of 159–1447 mm year −1 . Controlling grazing could, theoretically, slow or halt the movement of the contamination plume by allowing the shrub community to extract more water than is recharged in the aquifer.

Utah↗