Colorado River Research Articles

Decomposition of the mean absolute error (MAE) into systematic and unsystematic components.

When evaluating the performance of quantitative models, dimensioned errors often are characterized by sums-of-squares measures such as the mean squared error (MSE) or its square root, the root mean squared error (RMSE). In terms of quantifying average error, however, absolute-value-based measures such as the mean absolute error (MAE) are more interpretable than MSE or RMSE. Part of that historical preference for sums-of-squares measures is that they are mathematically amenable to decomposition and one can then form ratios, such as those based on separating MSE into its systematic and unsystematic components. Here, we develop and illustrate a decomposition of MAE into three useful submeasures: (1) bias error, (2) proportionality error, and (3) unsystematic error. This three-part decomposition of MAE is preferable to comparable decompositions of MSE because it provides more straightforward information on the nature of the model-error distribution. We illustrate the properties of our new three-part decomposition using a long-term reconstruction of streamflow for the Upper Colorado River.

Diverse Microbial Hot Spring Mat Communities at Black Canyon of the Colorado River.

The thermophilic microbial mat communities at hot springs in the Black Canyon of the Colorado River, thought to harbor the protistan human pathogen Naegleria fowleri, were surveyed using both culture-independent and -dependent methods to further understand the ecology of these hot spring microbiomes. Originating from Lake Mead source water, seven spring sites were sampled, varying in temperature from 25 to 55 °C. Amplicon-based high-throughput sequencing of twelve samples using 16S rRNA primers (hypervariable V4 region) revealed that most mats are dominated by cyanobacterial taxa, some but not all similar to those dominating the mats at other studied hot spring systems. 18S rRNA amplicon sequencing (V9 region) demonstrated a diverse community of protists and other eukaryotes including a highly abundant amoebal sequence related to Echinamoeba thermarum. Additional taxonomic and diversity metric analyses using near full-length 16S and 18S rRNA gene sequencing allowed a higher sequence-based resolution of the community. The mat sequence data suggest a major diversification of the cyanobacterial orders Leptolyngbyales, as well as microdiversity among several cyanobacterial taxa. Cyanobacterial isolates included some representatives of ecologically abundant taxa. A Spearman correlation analysis of short-read amplicon sequencing data supported the co-occurrences of populations of cyanobacteria, chloroflexi, and bacteroidetes providing evidence of common microbial co-occurrences across the Black Canyon hot springs.

Decoupling Urban Water Use from Population Growth in the Colorado River Basin

Decreases in river flows and rapidly declining reservoir levels pose grave water security risks to urban water utilities reliant upon the Colorado River Basin. This study evaluated multidecadal trends (2000–2020) in urban water use for 28 utilities with a combined service population of 23 million people that depend in part or wholly upon water supplies from the river and its tributaries. It was found that more than half of cities surveyed have substantially decoupled their water demands from population growth by greatly reducing their per capita water use. Total water deliveries to the cities surveyed dropped by 18% even though their combined service population increased by 24%. Median per capita water-use rates for total and residential use decreased by 30% and 28%, respectively. The most common water conservation strategies included toilet replacement rebates and other plumbing retrofits, variable water-pricing structures, and turf removal. Given considerable variability in total per capita water use and rate of per capita reductions, many cities should be able to substantially reduce water demands to attain the per capita water-use levels of top performers. In contrast with overall declines in water use, utilization of the Colorado River Basin as a water source has not declined but instead increased by 1%. These results suggest that opportunity may exist for reducing pressure on the Colorado River Basin if per capita water-use rates continue to decline and utilities increase their use of other water sources—including water reuse, desalination, and stormwater capture as well as other rivers and aquifers—that can be prioritized over the use of Colorado River supplies.

Correction to: “Whenever we exist on any land, we know it is our country”: Cocopa Mobility and the Colorado River in the U.S.-Mexico Borderlands, 1887–1936

Correction to: “Whenever we exist on any land, we know it is our country”: Cocopa Mobility and the Colorado River in the U.S.-Mexico Borderlands, 1887–1936

Exploring the Consistency of Water Scarcity Inferences between Large-Scale Hydrologic and Node-Based Water System Model Representations of the Upper Colorado River Basin

Water resources model development and simulation efforts have seen rapid growth in recent decades to aid evaluations and planning around water scarcity and allocation. Models are typically developed by two distinct communities: (1) large-scale hydrologic modelers emphasizing hydroclimatological processes, and (2) water systems modelers emphasizing environmental, infrastructural, and institutional features that shape water scarcity at the local basin level. This study assesses whether two representative models from these communities produce consistent insights when evaluating the water scarcity vulnerabilities in the Upper Colorado River Basin within the state of Colorado. Results showed that although the regional-scale model [model for scale adaptive river transport (MOSART)—water management (WM)] can capture the aggregate effect of all water operations in the basin, it underestimates the subbasin-scale variability in specific user’s vulnerabilities. The basin-scale water systems model [State of Colorado’s Stream Simulation Model (StateMod)] suggests a larger variance of scarcity across the basin’s water users due to its more detailed accounting of local water allocation infrastructure and institutional processes. This model intercomparison highlights potentially significant limitations of large-scale studies in seeking to evaluate water scarcity and actionable adaptation strategies, as well as ways in which basin-scale water systems model’s information can be used to better inform water allocation and shortage when used in tandem with larger-scale hydrological modeling studies.

Defining Regional and Local Sediment Sources in the Ancestral Colorado River System: A Heavy Mineral Study of a Mixed Provenance Unit in the Fish Creek-Vallecito Basin, Southern California

The Colorado River has flowed across the dextral strike-slip plate boundary between the North American and Pacific plates since the latest Miocene or earliest Pliocene. The Fish Creek-Vallecito Basin (FCVB) lies on the Pacific Plate in southern California, dextrally offset from the point where the modern Colorado river enters the Salton Trough; it contains a record of ancestral Colorado River sedimentation from 5.3–2.5 Ma. The basin stratigraphy exhibits a changing balance between locally derived (L-Suite) and Colorado River (C-Suite) sediments. This paper focuses on the Palm Springs Group (PSG), a thick fluvial and alluvial sequence deposited on the upper delta plain (between 4.2–2.5 Ma) when the Colorado was active in the area, allowing the detailed examination of the processes of sediment mixing from two distinct provenance areas. The PSG consists of three coeval formations: 1) Canebrake Conglomerate, a basin margin that has coarse alluvial fan deposits derived from surrounding igneous basement; 2) Olla Formation, fan-fringe sandstones containing L-Suite, C-Suite, and mixed units; and 3) Arroyo Diablo Formation, mineralogically mature C-Suite sandstones. Stratigraphic analysis demonstrates that the river flowed through a landscape with relief up to 2000 m. Satellite mapping and detailed logging reveal a variable balance between the two suites in the Olla Formation with an apparent upward increase in L-Suite units before abrupt cessation of Colorado sedimentation in the basin. Stable heavy mineral indices differentiate L-Suite (high rutile:zircon index: RZi 40–95) from C-Suite (RZi: 0–20). Both suites have garnet:zircon index (GZi) and apatite:tourmaline index (ATi) mostly above 50, although many L-suite and mixed Olla samples have much lower ATi (20–50), suggesting that the distal floodplain was wet and the local sediment had a longer residence time there, or went through several cycles of erosion and redeposition. Heavy mineral analysis, garnet geochemical analysis, and detrital zircon U-Pb age spectra allow us to quantify the amount of mixing from different sediment sources. These data show that about 30% of the mixed units are derived from the Colorado River and that up to 20% of the L-Suite is also derived from the Colorado River, suggesting that there was mutual cannibalisation of older deposits by fluvial channels in a transitional area at the basin margin. Although this study is local in scope, it provides an insight into the extent and nature of sediment mixing in a two-source system. We conclude that most ‘mixing’ is actually interbedding from separate sources; true mixing is facilitated by low subsidence rates and the rapid migration of fluvial channels.

High Resolution SnowModel Simulations Reveal Future Elevation‐Dependent Snow Loss and Earlier, Flashier Surface Water Input for the Upper Colorado River Basin

AbstractContinued climate warming is reducing seasonal snowpacks in the western United States, where >50% of historical water supplies were snowmelt‐derived. In the Upper Colorado River Basin, declining snow water equivalent (SWE) and altered surface water input (SWI, rainfall and snowmelt available to enter the soil) timing and magnitude affect streamflow generation and water availability. To adapt effectively to future conditions, we need to understand current spatiotemporal distributions of SWE and SWI and how they may change in future decades. We developed 100‐m SnowModel simulations for water years 2001–2013 and two scenarios: control (CTL) and pseudo‐global‐warming (PGW). The PGW fraction of precipitation falling as snow was lower relative to CTL, except for November–April at high elevations. PGW peak SWE was lower for low (−45%) and mid elevations (−14%), while the date of peak SWE was uniformly earlier in the year for all elevations (17–23 days). Currently unmonitored high elevation snow represented a greater fraction of total PGW SWE. PGW peak daily SWI was higher for all elevations (30%–42%), while the dates of SWI peaks and centroids were earlier in the year for all elevations under PGW. PGW displayed elevated winter SWI, lower summer SWI, and changes in spring SWI timing were elevation‐dependent. Although PGW peak SWI was elevated and earlier compared to CTL, SWI was more evenly distributed throughout the year for PGW. These simulated shifts in the timing and magnitude of SWE and SWI have broad implications for water management in dry, snow‐dominated regions.

Adaptive co-management and hydroclimatic change: examining the voluntary flow management program in the Upper Arkansas River Basin, Colorado

Adaptive co-management (ACM) has been advanced as a climate change adaptation strategy because of its social learning and collaboration dynamics. But it remains unclear whether ACM facilitates climate change adaptation in practice. Because rivers have been important laboratories for ACM efforts and research, this study examines a 30-year-old flow program on the Upper Arkansas River in Colorado (USA) to learn (a) how it is being impacted by climate change and (b) how participants are responding. The program has been largely successful in achieving its ecological and recreational flow goals, but it is being challenged by two hydroclimatic changes: earlier spring runoff and reduced stream flows. The program’s ACM dynamics are enabling adaptations that include efforts to communicate more proactively (social learning) and to compromise over the use of constrained flows (collaboration). We discuss these adaptations and pose additional questions about the future of the voluntary flow management program.

A 21st‐Century perspective on snow drought in the Upper Colorado River Basin

AbstractIn the Upper Colorado River Basin (UCRB), there is a deep reliance on seasonal snowpack for maintenance of water resources. The term “snow drought” has recently emerged to describe periods of anomalously low snowpack. Unique seasonal patterns in precipitation and temperature that drive snow drought can have distinct hydrologic signatures, and these relationships have not been carefully studied in the UCRB. Here we examine snow drought with a new classification scheme using peak snow water equivalent (SWE) and the ratio of basin‐wide modeled peak SWE to accumulated (onset to peak) precipitation (SWE/P) that clusters snow drought years into three distinct groups—“warm,” “dry,” and “warm & dry”—that minimize within‐group variance. Over the period 1916–2018, we identify 14 warm years ( = 160 mm; = 0.24), 24 dry years ( = 117 mm; = 0.35), and 21 warm & dry years ( = 94 mm; = 0.23). An elevation‐based analysis reveals two distinct patterns: warm snow droughts see severe SWE reductions primarily at lower (<2600 m) elevations (65% at lower elevations, 37% overall), whereas “dry” scenarios exhibit a consistent reduction across all elevations (39% overall). Using naturalized streamflow data, we also differentiate snow droughts by their earlier streamflow timing and decreased peakedness (warm: 7 days, 2%; dry: 7 days, 2%; warm & dry: 13 days, 5%). This research provides new insights into snow drought patterns relevant for regional water management.

Over half a century record of limnology data from Lake Powell, desert southwest United States: From reservoir filling to present day (1964–2021)

AbstractLake Powell is a large water storage reservoir in the arid southwestern United States. Here, we present a 58‐yr limnology dataset that captures water quality parameters from reservoir filling to present day (temperature, salinity, major ions, total suspended solids), as well as a 38‐yr record of Secchi depth, and a ~ 30‐yr record of nutrients, phytoplankton, and zooplankton assemblages. The dataset includes 5208 unique site visits spanning 258 unique sites of which 9 have been consistently visited. It also spans the establishment of an invasive bivalve (Dreissena bugensis, i.e. Quagga mussel) which was first detected in 2012. Given the general lack of long‐term data from lakes or reservoirs in arid regions, this dataset represents a unique contribution to regional, continental, and global‐scale limnology studies. As the hot drought in the desert southwest continues, we expect this dataset will inform water management decision‐making for this largest reservoir in the Upper Colorado River Basin.

ML-Based Streamflow Prediction in the Upper Colorado River Basin Using Climate Variables Time Series Data

Streamflow prediction plays a vital role in water resources planning in order to understand the dramatic change of climatic and hydrologic variables over different time scales. In this study, we used machine learning (ML)-based prediction models, including Random Forest Regression (RFR), Long Short-Term Memory (LSTM), Seasonal Auto- Regressive Integrated Moving Average (SARIMA), and Facebook Prophet (PROPHET) to predict 24 months ahead of natural streamflow at the Lees Ferry site located at the bottom part of the Upper Colorado River Basin (UCRB) of the US. Firstly, we used only historic streamflow data to predict 24 months ahead. Secondly, we considered meteorological components such as temperature and precipitation as additional features. We tested the models on a monthly test dataset spanning 6 years, where 24-month predictions were repeated 50 times to ensure the consistency of the results. Moreover, we performed a sensitivity analysis to identify our best-performing model. Later, we analyzed the effects of considering different span window sizes on the quality of predictions made by our best model. Finally, we applied our best-performing model, RFR, on two more rivers in different states in the UCRB to test the model’s generalizability. We evaluated the performance of the predictive models using multiple evaluation measures. The predictions in multivariate time-series models were found to be more accurate, with RMSE less than 0.84 mm per month, R-squared more than 0.8, and MAPE less than 0.25. Therefore, we conclude that the temperature and precipitation of the UCRB increases the accuracy of the predictions. Ultimately, we found that multivariate RFR performs the best among four models and is generalizable to other rivers in the UCRB.

Spatial attribution of declining Colorado River streamflow under future warming

Studies of climate change impacts in the Colorado River Basin have focused on the Upper Basin, finding that warming has exacerbated streamflow declines since 2000. Presently, it is unclear if the predicted high degree of interannual precipitation variability across the basin could overwhelm impacts of future warming and how this might vary in space. To address this, we employed an updated Variable Infiltration Capacity model framework to generate streamflow projections across the entire basin. Meteorological data were drawn from downscaled historical and future climate projections of eight climate models that best represent climatology. Results showed a high confidence of Far-Future (2066–2095) mean annual streamflow declines (relative to the Baseline, 1976–2005) at the Upper Basin, Lower Basin, and basin-wide scales (ensemble median trends of −5 % to −25 %). Streamflow declines were attributed to warming that diminished snowfall and melt during April to September and year-round increased soil evaporation from the Upper Basin, and overall precipitation declines in the Lower Basin. Widespread reductions in annual runoff and baseflow efficiencies indicated that precipitation increases did not offset the noted warming effects. Spatial coherence tests indicated that streamflow correlations among subbasins remained relatively constant in the future scenarios, though correlations with the Green River increased. This spatial attribution analysis is providing actionable information for water management in the Colorado River Basin under current and future conditions.

Human-Induced Resource Scarcity in the Colorado River Basin and Its Implications for Water Supply and the Environment in the Mexicali Valley Transboundary Aquifer

The Colorado River delta is a sedimentary alluvial formation that embodies the Lower Colorado River transboundary aquifer. The Mexicali Valley overlies the Mexican part of the aquifer, and the Imperial Valley the aquifer’s portion north of the Mexico–U.S. border. Mexico receives an annual water allocation from the Colorado River stipulated by an international treaty between Mexico and the United States. The Colorado River water allocation to Mexico is shared by farmers in the Mexicali Valley and by several border cities, rural communities, and industries in the northern region of the State of Baja California. Farmers withdraw groundwater from the Mexicali Valley’s aquifer to make up for insufficient Colorado River water to grow their crops. Groundwater withdrawal has created overdraft of the Mexicali Valley aquifer with associated adverse impacts: sea water intrusion, declining groundwater levels, upwelling of brackish groundwater, land subsidence, degradation of groundwater-dependent ecosystems, and emigration of displaced farmers. This article reviews the natural and human histories in the Colorado River basin and the Mexicali Valley, and presents a methodology applying remote sensing, geographic information analysis, and hydrologic analysis to calculate the annual water deficit in the Mexicali Valley. Finally, this work evaluates the valley’s annual water deficit in reference to current agricultural and socioeconomic trends observed in the study region. Aquifer and related environmental degradation have adversely affected small-scale farming and exacerbated demographic instability.

Tributary Voices: Literary and Rhetorical Explorations of the Colorado River. By Paul A. Formisano

Tributary Voices: Literary and Rhetorical Explorations of the Colorado River. By Paul A. Formisano

A Small Warm Tributary Provides Prespawning Resources for Colorado Pikeminnow in a Cold Dam-Regulated River

Abstract Riverine habitat mosaics, including tributaries, are an important reason the Green River subbasin supports the largest remaining population of federally endangered Colorado Pikeminnow Ptychocheilus lucius in the Colorado River Basin. Upstream Colorado Pikeminnow distribution is limited by Flaming Gorge Dam and few typically occurred in the reach immediately downstream of the dam, which is the reach most affected by thermal and hydrologic alterations. However, fish captures and passive integrated transponder (PIT) antenna sampling of previously tagged individuals from 2011 to 2021 revealed seasonal congregations of up to 75 Colorado Pikeminnow annually in the mouth of Vermillion Creek, a small tributary in the regulated reach. Approximately 11% (N = 93 individuals) of the entire 2017–2018 Green River basin population were encountered in Vermillion Creek over the 11-y study, an underestimate of use considering that untagged fish were not detected by antennas. Colorado Pikeminnow used Vermillion Creek primarily when Green River spring flows from Flaming Gorge Dam were high and cold in May through mid-June when the confluence was a large, deep backwater warmer than the main channel and supported forage fishes. Intra-annual encounters revealed seasonal residence times for individual Colorado Pikeminnow up to 91 d, and multiple inter-annual encounters indicated site fidelity. Frequent detections of individual Colorado Pikeminnow in a Yampa River spawning area soon after their detections in Vermillion Creek indicate this tributary may be an important resource for reproductive adults. The intensive and basin-wide PIT tagging and detection program for Colorado Pikeminnow enhanced our understanding of the importance of small habitat nodes such as Vermillion Creek in the Green River drainage network. Understanding and protecting these seasonally available riverine habitat mosaics used for prespawning conditioning may assist with recovery of Colorado Pikeminnow.

Institutional levels of water management in the Colorado River basin region: A macro-historical geographic review

Complex water-stressed basins like the Colorado River in North America have multiple institutional levels of water management. Each institutional level is characterized by rules, organizations, and spatial jurisdictions that developed over decades to centuries to shape a dynamic multi-level system. After introducing the concept of institutional levels, and its relationship to geographic scales, this paper employs systematic bibliographic search methods to review their development in the Colorado River basin region. Results begin with the community level of water management from prehistoric Indian water cultures to early Hispanic water communities, 19th century water communities, and 20th century water organizations. Conflict among water communities shaped the state level of constitutional authority over water rights administration during the 19th century. Competition among states led in the 20th century to the interstate level of apportionment that often paralleled federal and tribal level water development policies, eventually leading to the international level of treaty relations between the U.S. and Mexico. This macro-historical geographic progression from institutions that were relatively small in size and early in time to those at higher levels and more recent in time offers insights into the multi-level institutional logic of the “law of the river” in the Colorado River basin region.

Operational water forecast ability of the HRRR-iSnobal combination: an evaluation to adapt into production environments

Abstract. Operational water-resource forecasters, such as the Colorado Basin River Forecast Center (CBRFC) in the Western United States, currently rely on historical records to calibrate the temperature-index models used for snowmelt runoff predictions. This data dependence is increasingly challenged, with global and regional climatological factors changing the seasonal snowpack dynamics in mountain watersheds. To evaluate and improve the CBRFC modeling options, this work ran the physically based snow energy balance iSnobal model, forced with outputs from the High-Resolution Rapid Refresh (HRRR) numerical weather prediction model across 4 years in a Colorado River Basin forecast region. Compared to in situ, remotely sensed, and the current operational CBRFC model data, the HRRR-iSnobal combination showed well-reconstructed snow depth patterns and magnitudes until peak accumulation. Once snowmelt set in, HRRR-iSnobal showed slower simulated snowmelt relative to observations, depleting snow on average up to 34 d later. The melting period is a critical component for water forecasting. Based on the results, there is a need for revised forcing data input preparation (shortwave radiation) required by iSnobal, which is a recommended future improvement to the model. Nevertheless, the presented performance and architecture make HRRR-iSnobal a promising combination for the CBRFC production needs, where there is a demonstrated change to the seasonal snow in the mountain ranges around the Colorado River Basin. The long-term goal is to introduce the HRRR-iSnobal combination in day-to-day CBRFC operations, and this work created the foundation to expand and evaluate larger CBRFC domains.

Crevasse splay morphodynamics near a non-vegetated, ephemeral river terminus: Insights from process-based modelling

Crevasse splays generate subtle local relief and contribute to fluvial basin sedimentary filling but controls on splay development along dryland rivers remain poorly understood owing to limited field, laboratory, and numerical modelling studies. Based on previously-acquired field data and new remote sensing observations of splay morphology and sedimentology (e.g. slope, width, length, grain size) and flooding characteristics (e.g. discharge, water depth and extent) near the terminus of the non-vegetated, ephemeral Río Colorado on the southeastern margin of Salar de Uyuni, Bolivia, we undertake process-based modelling using Delft3D to isolate the role of hydrological controls on crevasse splay morphodynamics. Holding the potential sediment supply constant, we focus on the role of discharge (outflow from trunk channel to crevasse channel during rising stage), floodplain water levels, and backflow (reflux to the trunk channel during falling stage). Using nine different model runs, each with 10 simulated flood cycles, we show that the processes associated with these hydrological controls result in various outcomes, from short crevasse splay channels that may bifurcate and develop depositional bars to longer splays with one primary channel that mainly transfers sediment across the floodplain. Results reveal that increases in flood discharge lead to more rapid splay sedimentation and stabilization of a single crevasse channel. Increases in floodplain water level lead to shorter but wider splays and facilitate the formation of multiple stable crevasse channels. High floodplain water levels probably restrict splay length owing to deceleration of outflow as floodplain water is encountered, but separate crevasse channels may form downstream as backflow breaches the trunk channel levee during falling stage. These findings support and extend previous observations from the Río Colorado and other dryland rivers worldwide. Future modelling studies that consider a wider range of hydrological, sedimentological, and floodplain topographic conditions will help develop more comprehensive numerical models of splay development. A combination of insights from field, laboratory experimentation, remote sensing and modelling will improve knowledge of the cascades of channel-floodplain dynamics that characterise many dryland endorheic basins.

R-statistic based predictor variables selection and vine structure determination approach for stochastic streamflow generation considering temporal and spatial dependence

Stochastic streamflow generation is crucial for water resources planning and management as well as water conservancy project design and operation. This study proposes an accurate, reliable and parsimonious approach for stochastic streamflow generation considering temporal and spatial dependence on the basis of regular vine copula model. The emphasis is on advancing an R-statistic based strategy of vine structure determination that divide the vine copula model construction into two independent parts and avoid continuous accumulation of uncertainty in the traditional Kendall's tau based method. Two study regions (the Upper Colorado River basin and Middle Yangtze River basin) with diverse hydrology regime and available data length are selected as case studies to showcase the performance of the proposed approach in practice. The results indicate better performance than two existing models in terms of streamflow estimation, and demonstrate that stochastic simulation series can preserve distribution and statistical characteristics of observed records. R-vine copula model constructed by the proposed approach is confirmed to possess low sensitivity to the number of predictor variables as well as good adaptability and robustness to streamflow series with diverse characteristics and abundances. The enhanced capability and performance stem from the accurate identification of predictor variables and characterization of complex and diverse dependence structures among different streamflow series, on the basis of a comprehensive and precise dependence measure, R-statistic.

Wear the Blue Star: Frontier Values vs. Environmentalism in News Coverage of Colorado River Dams, 1954-1956

ABSTRACT This study examines news coverage of a federal project that resulted in the building of Glen Canyon Dam on the Colorado River and sparked an environmental controversy. The project pitted boosters against conservationists, and this research illustrates how western newspapers promoted growth through dams and irrigation. Acknowledging the region in which several newspapers operated, this study uses New Western History to better understand journalism history by highlighting the harsh landscape and the persistence of pioneer values in the 1950s. This research also introduces a new element of environmental journalism history by adding to understanding of such reporting in the 1950s and by approaching the dam controversy from the perspective of journalism rather than environmentalism. Whether newspapers focused on growth and prosperity or preserving natural beauty, their coverage reflected the complexity of the region and its ecosystem.