General Circulation Model Results Research Articles

A mini-chemical scheme with net reactions for 3D general circulation models

Context. The chemical inventory of hot Jupiter (HJ) exoplanet atmospheres continues to be observed by various ground- and space-based instruments in increasing detail and precision. It is expected for some HJs to exhibit strong non-equilibrium chemistry characteristics in their atmospheres, which might be inferred from spectral observations. Aims. We aim to model the 3D thermochemical non-equilibrium chemistry in the atmospheres of the HJs WASP-39b and HD 189733b. Methods. We coupled a lightweight, reduced chemical network ‘mini-chem’ that utilises net reaction rate tables to the Exo-FMS general circulation model (GCM). We performed GCM models of the exoplanets WASP-39b and HD 189733b as case studies of the coupled mini-chem scheme. The GCM results were then post-processed using the 3D radiative-transfer model gCMCRT to produce transmission and emission spectra to assess the impact of non-equilibrium chemistry on their observable properties. Results. Both simulations show significant departures from chemical equilibrium (CE) due to the dynamical motions of the atmosphere. The spacial distribution of species generally closely follows the dynamical features of the atmosphere rather than the temperature field. Each molecular species exhibits a different quench level in the simulations, which is also dependent on the latitude of the planet. Major differences are seen in the transmission and emission spectral features between the CE and kinetic models. Conclusions. Our simulations indicate that considering the 3D kinetic chemical structures of HJ atmospheres has an important impact on the physical interpretation of observational data. Drawing bulk atmospheric parameters from fitting feature strengths may lead to an inaccurate interpretation of chemical conditions in the atmosphere of HJs. Our open source mini-chem module is simple to couple with contemporary HJ GCM models without substantially increasing required computational resources.

Late Triassic paleowinds from lacustrine wave ripple marks in the Fleming Fjord Group, central East Greenland

Geological evidence of paleoclimate conditions provide important constraints on paleoclimate models. Paleowinds are one of the central paleoclimate parameters in global circulation models used to reconstruct past climatic conditions. However, only a few climate proxies such as eolian dunes and shallow-water wave ripples provide information on paleowind directions. In this study, we present new paleoclimatic data based on lacustrine sediments with wave ripple marks in the Upper Triassic Fleming Fjord Group, central East Greenland deposited at very shallow water depth in the northern part of Pangaea in a mid-latitude, warm-temperate climate. Wave-ripple orientations are measured on 380 individual fossilized wave-rippled beds at four localities in the ~8500 km 2 lacustrine basin. These ripple data are used to establish a geologic wind proxy and are compared to previously published general circulation models. Two wave ripple orientations are observed: The dominant ripple orientation and wave ripple characteristics indicate paleowinds from the Late Triassic SSE and NNW (154.5° and 334.5°), while a subordinate orientation indicate paleowinds from W or E (270° or 90°). This paleowind regime remained stable for at least ~7.5 million years during the mid-late Norian (218.5-211 Ma). These results correspond very well with some general circulation model results that suggest summer winds from the NNW and winter winds from the SSE. Based on the great compatibility between empirical data and general circulation model results, the wind pattern seems to have been greatly influenced by regional, Late Triassic mountain topography in the present-day Greenland and Norway channeling the paleowind in the northernmost part of the pre-Atlantic rift basin (the mid-Norwegian-east Greenland rift system).

Global Surface Temperature Response to 11-Yr Solar Cycle Forcing Consistent with General Circulation Model Results

ABSTRACTThe 11-yr solar cycle is associated with a roughly 1 W m−2 trough-to-peak variation in total solar irradiance and is expected to produce a global temperature response. The sensitivity of this response is, however, contentious. Empirical best estimates of global surface temperature sensitivity to solar forcing range from 0.08 to 0.18 K (W m−2)−1. In comparison, best estimates from general circulation models forced by solar variability range between 0.03 and 0.07 K (W m−2)−1, prompting speculation that physical mechanisms not included in general circulation models may amplify responses to solar variability. Using a lagged multiple linear regression method, we find a sensitivity of global-average surface temperature ranging between 0.02 and 0.09 K (W m−2)−1, depending on which predictor and temperature datasets are used. On the basis of likelihood maximization, we give a best estimate of the sensitivity to solar variability of 0.05 K (W m−2)−1 (0.03–0.09 K; 95% confidence interval). Furthermore, through updating a widely used compositing approach to incorporate recent observations, we revise prior global temperature sensitivity best estimates of 0.12–0.18 K (W m−2)−1 downward to 0.07–0.10 K (W m−2)−1. The finding of a most likely global temperature response of 0.05 K (W m−2)−1 supports a relatively modest role for solar cycle variability in driving global surface temperature variations over the twentieth century and removes the need to invoke processes that amplify the response relative to that exhibited in general circulation models.

Long-Term Development Prospects of Russia’s Wind Energy in the Conditions of Expected Climate Changes

The climatic effect on the operation of wind power plants in Russia is analyzed. Based on the global experience of wind farms’ operation, a quantitative assessment of the sensitivity of electric power generation by modern wind turbines to wind speed variation is carried out. Using the ensemble approach, predictive estimates of changes in the wind fields in Russia are obtained for the 21st century using the results of general atmospheric circulation models participating in the international project CMIP5 (Coupled Multimodel Intercomparison Project Phase 5). The validity of the findings is ensured by the validation procedure, including a comparison of different versions of the multimodel ensemble with data reanalysis. The predictive estimate obtained for the climatic scenario developed at the National Research University Moscow Power Engineering Institute (NRU MPEI) is compared with generally accepted climatic scenarios based on the use of so-called greenhouse gas representative concentration pathways. It is shown that the choice of the scenario has a significant impact on the forecast results. However, the data of the calculations distinguish several features of the wind regime in the 21st century, which are almost independent of the selected scenario or ensemble composition and, apparently, can be considered reliable. In particular, it is found that there is a possibility of some decrease in average wind speeds across Russia during the 21st century. However, in Primorskiy Kray, the expected climate change will lead to the formation of a zone with a steady increase in its speed. Changes in the technical wind potential in the regions of the country where the construction of wind turbines is planned will amount to from –15 to –20% for the subarctic regions and from +5 to +10% for Primorskiy Kray by the end of the 21st century. It follows from the calculations that the currently observed climate warming, in all likelihood, does not pose a serious threat to the development of wind energy in Russia. The modern and planned location of wind farms even makes it possible to expect some growth in their production rate in the first half of the 21st century. At the same time, the prospect of long-term changes in the wind regime should certainly be taken into account when selecting the wind farm location and predesign analysis as part of the measures aimed at adapting to climate changes.

Dim Prospects for Transmission Spectra of Ocean Earths around M Stars

Abstract The search for water-rich Earth-sized exoplanets around low-mass stars is rapidly gaining attention because they represent the best opportunity to characterize habitable planets in the near future. Understanding the atmospheres of these planets and determining the optimal strategy for characterizing them through transmission spectroscopy with our upcoming instrumentation is essential in order to constrain their environments. For this study, we present simulated transmission spectra of tidally locked Earth-sized ocean-covered planets around late-M to mid-K stellar spectral types, utilizing the results of general circulation models previously published by Kopparapu et al. as inputs for our radiative transfer calculations performed using NASA’s Planetary Spectrum Generator (psg.gsfc.nasa.gov). We identify trends in the depth of H2O spectral features as a function of planet surface temperature and rotation rate. These trends allow us to calculate the exposure times necessary to detect water vapor in the atmospheres of aquaplanets through transmission spectroscopy with the upcoming James Webb Space Telescope as well as several future flagship space telescope concepts under consideration (the Large UV Optical Infrared Surveyor and the Origins Space Telescope) for a target list constructed from the Transiting Exoplanet Survey Satellite (TESS) Input Catalog (TIC). Our calculations reveal that transmission spectra for water-rich Earth-sized planets around low-mass stars will be dominated by clouds, with spectral features <20 ppm, and only a small subset of TIC stars would allow for the characterization of an ocean planet in the habitable zone. We thus present a careful prioritization of targets that are most amenable to follow-up characterizations with next-generation instrumentation, in order to assist the community in efficiently utilizing precious telescope time.

Retrieval of Martian ozone and dust from SPICAM spectrometer for MY27–MY28

Ozone \((\hbox {O}_{3})\) is important in the stabilisation of \(\hbox {CO}_{{2}}\) in the Martian atmosphere and thus it is important to study the spatio-temporal variability of \(\hbox {O}_{{3}}\). We retrieve two years of total columnar \(\hbox {O}_{{3}}\) from raw spectral data provided by the SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument aboard the Mars Express. The seasonal variability is studied in tropical, mid- and high latitudes and is compared with simulations by a photochemical coupled general circulation model (GCM). The high latitudes exhibit the largest seasonal variations in \(\hbox {O}_{{3}}\), with a winter high and a summer low and a comparison with GCM results is good in general. We have studied the correlation of \(\hbox {O}_{{3}}\) with dust, retrieved simultaneously from SPICAM observations. In southern tropical latitudes, the columnar \(\hbox {O}_{{3}}\) is seen to increase during a global dust storm year (Martian year (MY) 28) compared to the \(\hbox {O}_{{3}}\) column values during a year without global dust storm (MY27), although the water vapour column between these years remains unchanged. This indicates the radiative impact of dust on \(\hbox {O}_{{3}}\) and its retrieval. We also study the ozone–carbon monoxide correlation as a tracer of dynamics. The dynamical contribution to the \(\hbox {O}_{{3}}\) column is found to be the highest during winter over the southern polar region.

Local Time Dependence of the Thermal Structure in the Venusian Equatorial Upper Atmosphere: Comparison of Akatsuki Radio Occultation Measurements and GCM Results

AbstractTemperature profiles of the Venus atmosphere obtained by the Akatsuki radio occultation measurements showed a prominent local time dependence above 65‐km altitude at low latitudes equatorward of 35°. A zonal wavenumber 2 component is predominant in the temperature field, and its phase (i.e., isothermal) surfaces descend with local time, suggesting its downward phase propagation. A general circulation model (GCM) for the Venus atmosphere, AFES‐Venus, reproduced the local time‐dependent thermal structure qualitatively consistent with the radio occultation measurements. Based on a comparison between the radio occultation measurements and the GCM results, the observed zonal wavenumber 2 structure is attributed to the semidiurnal tide. Applying the dispersion relationship for internal gravity waves to the observed wave structure, the zonally averaged zonal wind speed at 75‐ to 85‐km altitudes was found to be significantly smaller than that at the cloud top. The decrease of the zonal wind speed with altitude is attributed to the momentum deposition by the upwardly propagating semidiurnal tide excited in the cloud layer.

Ocean Circulation in the Toarcian (Early Jurassic): A Key Control on Deoxygenation and Carbon Burial on the European Shelf

AbstractThe Toarcian Oceanic Anoxic Event (T‐OAE, ∼183 Myr) was a long‐lasting episode of ocean deoxygenation during the Early Jurassic. The event is related to a period of global warming and characterized by major perturbations to the hydrological and carbon cycles with high rates of organic matter burial in shelf seas. Ocean circulation during the Toarcian and its influence on marine biogeochemical cycles are still not fully understood. Here we assess the spatial extent of anoxia in the NW Tethys Ocean during the T‐OAE, the relationship with ocean circulation and the impact on organic carbon burial, using new and existing sedimentary records from the European Epicontinental Shelf in combination with general circulation model results. We demonstrate that bottom waters on the southwestern part of the shelf were mainly oxic during the T‐OAE, while those in the northeastern basins were mostly anoxic or even sulfidic. Results for two ocean‐atmosphere models (Fast Ocean‐Atmosphere Model and Massachusetts Institute of Technology general circulation model) suggest the presence of a strong clockwise gyre over the European Epicontinental Shelf, which brought oxygenated equatorial waters from the Tethys Ocean to the southern shelf. The northward limb of the gyre was significantly weakened due to the rough bathymetry of the northern shelf, making this relative small region highly sensitive to local ocean stratification. These sluggish ocean dynamics promoted bottom water anoxia and enhanced burial of organic carbon in the northeastern basins, which accounted for 3–5% of the total carbon extracted from the ocean‐atmosphere system as recorded by the positive carbon isotope shift.

Estimation of hydrological response to future climate change in a cold watershed

Abstract The vulnerability of the natural water system in cold areas to future climate change is of great concern. A coupled model approach was applied in the headwater watershed area of Yalu River in the northeastern part of China to estimate the response of hydrological processes to future climate change with moderate data. The stochastic Long Ashton Research Station Weather Generator was used to downscale the results of general circulation models to generate synthetic daily weather series in the 2050s and 2080s under various projected scenarios, which were applied as input data of the Generalized Watershed Loading Functions hydrological model for future hydrological process estimations. The results showed that future wetter and hotter weather conditions would have positive impacts on the watershed runoff yields but negative impacts on the watershed groundwater flow yields. The freezing period in winter would be shortened with earlier snowmelt peaks in spring. These would result in less snow cover in winter and shift the monthly allocations of streamflow with more yields in March but less in April and May, which should be of great concern for future local management. The proposed approach of the coupled model application is effective and can be used in other similar areas.

Defining spatiotemporal characteristics of climate change trends from downscaled GCMs ensembles: how climate change reacts in Xinjiang, China

ABSTRACTThe fragile ecosystem, scarce water resources, and limited ecosystem resilience of Xinjiang, China make the region especially vulnerable to climate change. Researchers need reliable analyses of climate change trends to formulate regional mitigation and adaption strategies and to support sustainable development. Therefore, two statistical downscaling methods and the combination of a Mann–Kendall test with Co‐Kriging interpolation were used to investigate the spatiotemporal characteristics of climate change in Xinjiang based on the ensemble of 37 general circulation models (GCMs) in 2021–2060. The reliabilities of single run and ensemble downscaling results of GCMs were evaluated by 69 meteorological stations over the period 1965–2004. The correlation coefficients (CC) with the observations for precipitation and temperature ranged between 0.4–0.8 and 0.9–0.99 in the reference period, respectively. CC improved to 0.87 and was close to 1 after downscaling for precipitation and temperature, respectively. A pronounced increase of ca. 0.27–0.51 °C decade−1 was projected overall, and especially for Representative Concentration Pathway (RCP) 8.5 in northern Xinjiang. In general, the precipitation changed by −1.66 to 6.83% decade−1 while varying seasonally and spatially; a declining tendency emerged in the western regions of Xinjiang during summer. More extreme rainfall events are predicted to occur in summer and autumn months, while warmer extremes would be concentrated in August. The climate in Xinjiang will continue to become warmer and wetter. Nevertheless, Western Xinjiang will experience a warmer and drier climate in summer and autumn. These projections of climate change in the near future are able to provide useful information for the development of potential mitigation measures and adaptation strategies. Multiple circulation mechanisms are also suggested accounting for the changes in precipitation and temperature which will benefit the understanding of the possible drivers of climate variability in this region.

What model resolution is required in climatological downscaling over complex terrain?

This study presents results from the Weather Research and Forecasting (WRF) model applied for climatological downscaling simulations over highly complex terrain along the Eastern Mediterranean. We sequentially downscale general circulation model results, for a mild and wet year (2003) and a hot and dry year (2010), to three local horizontal resolutions of 9, 3 and 1km. Simulated near-surface hydrometeorological variables are compared at different time scales against data from an observational network over the study area comprising rain gauges, anemometers, and thermometers. The overall performance of WRF at 1 and 3km horizontal resolution was satisfactory, with significant improvement over the 9km downscaling simulation. The total yearly precipitation from WRF's 1km and 3km domains exhibited <10% bias with respect to observational data. The errors in minimum and maximum temperatures were reduced by the downscaling, along with a high-quality delineation of temperature variability and extremes for both the 1 and 3km resolution runs. Wind speeds, on the other hand, are generally overestimated for all model resolutions, in comparison with observational data, particularly on the coast (up to 50%) compared to inland stations (up to 40%). The findings therefore indicate that a 3km resolution is sufficient for the downscaling, especially that it would allow more years and scenarios to be investigated compared to the higher 1km resolution at the same computational effort. In addition, the results provide a quantitative measure of the potential errors for various hydrometeorological variables.

Vertical structure of the axi‐asymmetric temperature disturbance in the Venusian polar atmosphere: Comparison between radio occultation measurements and GCM results

AbstractVertical temperature profiles at 40–75 km around 80°N in the Venus polar vortex are retrieved over 13 Earth days almost continuously from radio occultation measurements (Venus Express radio occultation) in the Venus Express mission. They show periodical variations with a dominant period of ∼3.1 Earth days. These fluctuations are confined in an altitude range of 45–65 km with a local minimum at ∼58 km altitude, where the static stability abruptly increases with height. The phase of the temperature fluctuations is almost reversed at the 58 km level and varies little above and below this altitude. A numerical simulation of a Venusian atmospheric general circulation model (GCM) shows that the axi‐asymmetric temperature disturbance with zonal wave number 1 is predominant at 50–75 km levels in the model atmosphere. The vertical structure of the reproduced disturbance agrees quite well with that retrieved by the radio occultation measurement: amplitude of the temperature fluctuation has a local minimum and its phase is reversed at the altitude (65 km in the model) where the static stability rapidly changes as in the observations. Above and below this altitude, the phase is almost constant in the vertical direction. The relationship among the temperature, horizontal winds, and geopotential height associated with the simulated disturbance suggests that the axi‐asymmetric temperature disturbance observed in the Venus polar region can be interpreted as neutral barotropic Rossby waves related to barotropic instability in the polar region.

Comparison of Statistical Downscaling Methods for Monthly Total Precipitation: Case Study for the Paute River Basin in Southern Ecuador

Downscaling improves considerably the results of General Circulation Models (GCMs). However, little information is available on the performance of downscaling methods in the Andean mountain region. The paper presents the downscaling of monthly precipitation estimates of the NCEP/NCAR reanalysis 1 applying the statistical downscaling model (SDSM), artificial neural networks (ANNs), and the least squares support vector machines (LS-SVM) approach. Downscaled monthly precipitation estimates after bias and variance correction were compared to the median and variance of the 30-year observations of 5 climate stations in the Paute River basin in southern Ecuador, one of Ecuador’s main river basins. A preliminary comparison revealed that both artificial intelligence methods, ANN and LS-SVM, performed equally. Results disclosed that ANN and LS-SVM methods depict, in general, better skills in comparison to SDSM. However, in some months, SDSM estimates matched the median and variance of the observed monthly precipitation depths better. Since synoptic variables do not always present local conditions, particularly in the period going from September to December, it is recommended for future studies to refine estimates of downscaling, for example, by combining dynamic and statistical methods, or to select sets of synoptic predictors for specific months or seasons.

Incremental dynamical downscaling for probabilistic analysis based on multiple GCM projections.

A dynamical downscaling method for probabilistic regional‐scale climate change projections was developed to cover the inherent uncertainty associated with multiple general circulation model (GCM) climate simulations. The climatological increments estimated by GCM results were statistically analyzed using the singular vector decomposition. Both positive and negative perturbations from the ensemble mean with the magnitudes of their standard deviations were extracted and added to the ensemble mean of the climatological increments. The analyzed multiple modal increments were utilized to create multiple modal lateral boundary conditions for the future climate regional climate model (RCM) simulations by adding them to reanalysis data. The incremental handling of GCM simulations realized approximated probabilistic climate change projections with the smaller number of RCM simulations. For the probabilistic analysis, three values of a climatological variable simulated by RCMs for a mode were analyzed under an assumption of linear response to the multiple modal perturbations.

Attributing the behavior of low‐level clouds in large‐scale models to subgrid‐scale parameterizations

AbstractThis study explores ways of establishing the characteristic behavior of boundary layer schemes in representing subtropical marine low‐level clouds in climate models. To this purpose, parameterization schemes are studied in both isolated and interactive mode with the larger‐scale circulation. Results of the EUCLIPSE/GASS intercomparison study for Single‐Column Models (SCM) on low‐level cloud transitions are compared to General Circulation Model (GCM) results from the CFMIP‐2 project at selected grid points in the subtropical eastern Pacific. Low cloud characteristics are plotted as a function of key state variables for which Large‐Eddy Simulation results suggest a distinct and reasonably tight relation. These include the Cloud Top Entrainment Instability (CTEI) parameter and the total cloud cover. SCM and GCM results are thus compared and their resemblance is quantified using simple metrics. Good agreement is reported, to such a degree that SCM results are found to be uniquely representative of their GCM, and vice versa. This suggests that the system of parameterized fast boundary layer physics dominates the model state at any given time, even when interactive with the larger‐scale flow. This behavior can loosely be interpreted as a unique “fingerprint” of a boundary layer scheme, recognizable in both SCM and GCM simulations. The result justifies and advocates the use of SCM simulation for improving weather and climate models, including the attribution of typical responses of low clouds to climate change in a GCM to specific parameterizations.

New observations of molecular nitrogen in the Martian upper atmosphere by IUVS on MAVEN

AbstractWe identify molecular nitrogen (N2) emissions in the Martian upper atmosphere using the Imaging Ultraviolet Spectrograph (IUVS) on NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We report the first observations of the N2 Lyman‐Birge‐Hopfield (LBH) bands at Mars and confirm the tentative identification of the N2 Vegard‐Kaplan (VK) bands. We retrieve N2 density profiles from the VK limb emissions and compare calculated limb radiances between 90 and 210 km against both observations and predictions from a Mars general circulation model (GCM). Contrary to earlier analyses using other satellite data, we find that N2 abundances exceed GCM results by about a factor of 2 at 130 km but are in agreement at 150 km. The analysis and interpretation are enabled by a linear regression method used to extract components of UV spectra from IUVS limb observations.

An Analysis of the Linkage of Pacific Subtropical Cells with the Recharge–Discharge Processes in ENSO Evolution

Abstract The Simple Ocean Data Assimilation, version 2.2.4 (SODA 2.2.4), analysis for the period of 1960–2010 is used to study the variability of Pacific subtropical cells (STCs) and its causal relation with tropical climate variability. Results show that the interior STC transport into the equatorial basin through 9°S and 9°N is well connected with equatorial sea surface temperature (SST) (9°S–9°N, 180°–90°W). The highest correlation at interannual time scales is contributed by the western interior STC transport within 160°E and 130°W. It is known that the ENSO recharge–discharge cycle experiences five stages: the recharging stage, recharged stage, warmest SST stage, discharging stage, and discharged stage. A correlation analysis of interior STC transport convergence, equatorial warm water volume (WWV), wind stress curl, and SST identifies the time intervals between the five stages, which are 8, 10, 2, and 8 months, respectively. A composite analysis for El Niño–developing and La Niña–developing events is also performed. The composited ENSO evolutions are in accordance with the recharge–discharge theory and the corresponding time lags between the above denoted five stages are 4–12, 6, 2, and 4 months, respectively. For stronger El Niño events, the discharge due to interior STC transport at 9°N terminates earlier than that at 9°S because of the southward migration of westerly winds following the El Niño peak phase. This study clarifies subsurface transport processes and their time intervals, which are useful for refinement of theoretical models and for evaluating coupled ocean–atmosphere general circulation model results.

Regional climate model projections of rainfall from U.S. landfalling tropical cyclones

The eastern United States is vulnerable to flooding from tropical cyclone rainfall. Understanding how both the frequency and intensity of this rainfall will change in the future climate is a major challenge. One promising approach is the dynamical downscaling of relatively coarse general circulation model results using higher-resolution regional climate models (RCMs). In this paper, we examine the frequency of landfalling tropical cyclones and associated rainfall properties over the eastern United States using Zetac, an 18-km resolution RCM designed for modeling Atlantic tropical cyclone activity. Simulations of 1980–2006 tropical cyclone frequency and rainfall intensity for the months of August–October are compared against results from previous studies and observation-based datasets. The 1980–2006 control simulations are then compared against results from three future climate scenarios: CMIP3/A1B (late twenty-first century) and CMIP5/RCP4.5 (early and late twenty-first century). In CMIP5 early and late twenty-first century projections, the frequency of occurrence of post-landfall tropical cyclones shows little net change over much of the eastern U.S. despite a decrease in frequency over the ocean. This reflects a greater landfalling fraction in CMIP5 projections, which is not seen in CMIP3-based projections. Average tropical cyclone rain rates over land within 500 km of the storm center increase by 8–17 % in the future climate projections relative to control. This is at least as much as expected from the Clausius–Clapeyron relation, which links a warmer atmosphere to greater atmospheric water vapor content. Over land, the percent enhancement of area-averaged rain rates from a given tropical cyclone in the warmer climate is greater for larger averaging radius (300–500 km) than near the storm, particularly for the CMIP3 projections. Although this study does not focus on attribution, the findings are broadly consistent with historical tropical cyclone rainfall changes documented in a recent observational study. The results may have important implications for future flood risks from tropical cyclones.

The Use of Statistical Weather Generator, Hybrid Data Driven and System Dynamics Models for Water Resources Management under Climate Change

Nowadays, the assumption of stationary patterns in hydrologic time series is being challenged, mainly because of climate change and the uncertainty brought about by it. In this paper, climate change and impacts on water resources of Zolachay in Urmia Lake basin in northwestern Iran have been studied comprehensively. Expected precipitation and temperature changes are obtained from the results of general circulation models (GCMs) approved by IPCC AR4 in three emission scenarios of A1B, A2, and B1. To simulate climate change conditions for horizon 2020, LARS-WG, as a stochastic weather generator, has been employed. Analyzing results by a Kernel density estimator indicates a decrease in annual precipitation and a tendency to a warmer climate. Then different data-driven models such as artificial neural network and M5 model tree, in conjunction with wavelet transform, have been used to develop a rainfall–runoff model of the basin on a monthly time scale. Results show that a warmer and drier climate in the future will cause the hydrograph to have temporal and quantitative changes. Operation of the multipurpose Zola Reservoir (located on the main stream) is simulated using the system dynamics approach. In addition to changes in the runoff of the basin, development scenario is also considered. Results demonstrate considerable changes in the reliability and deficiency measures in the operation of Zola Reservoir under climate change condition and development scenario. These results indicate that a revision in the rule curve of the reservoir is needed. Finally, this study predicts that more groundwater could be extracted to supply demands in the basin.

Climate Change Effects on Evapotranspiration in Mexico

In Mexico’s case, the scarcity of water in the north of the country is worrying, even more from the agricultural point of view because according to the results of general circulation models, a major impact due to global warming is expected in this region, and it will have important repercussions on the rural sector in the north of Mexico. According to [1] the results of the sensitivity analysis made in this study indicate that the most vulnerable zone is the north of Mexico, wherein the increase of evapotraspiration (ET) is greater in comparison to the rest of the country; up to 8% annual average for a +3°;C growth in mean annual temperature. Due to some limitations in this preliminary investigation (e.g., global temperature data was used without regionalizing it), it was decided to make more detailed studies to estimate the climate change effects on ET on a regional scale, using the downscaling method to adjust temperature data. In this study a new methodology to estimate the ET before climate change scenarios is introduced, which includes the selection of the Hargreaves-Samani method (HS), calibrated and compared against the Penman-Monteith ASCE method in various irrigation districts in the northern part of the country, obtaining ET estimations with a 93% precision. This procedure was applied to nine states in north Mexico: Baja California, Baja California Sur, Chihuahua, Sinaloa, Sonora, Tamaulipas, Nuevo Leon, Coahuila y Durango. The principal results are enunciated as follows: the ET variations between the contemporary scenario and the 2030 scenario are quite significant, according to the data of 160 meteorological stations; for temperature variations between 0.1°;C to 0.45°;C the corresponding ET fluctuation goes from 2% in the current scenario to 7% in the 2030 scenario. These obtained percentages are greater than the ones expected to happen for the precision of the method. It is important to note that a 7% rise of ET (related to a regional temperature increase of approximately one degree) would represent in practice having more millions of m3 of water in dams to satisfy the water demand of crops.