Change In Arid Regions Research Articles

Impacts of climate change on vegetation phenology and net primary productivity in arid Central Asia

Vegetation is highly sensitive to climate changes in arid regions. The relationship between vegetation and climate changes can be effectively characterized by vegetation phenology. However, few studies have examined the vegetation phenology and productivity changes in arid Central Asia (ACA). The vegetation phenological information of ACA was extracted using MODIS NDVI (Normalized Difference Vegetation Index) data, and the dynamics of vegetation phenological changes under spatiotemporal variations were quantitatively assessed. Moreover, the impacts of climate change on vegetation phenology and net primary productivity were analyzed by combining meteorological data with that of MODIS NPP (Net Primary Productivity) during the same period. The results demonstrated that the start of the season (SOS) of vegetation in the study was concentrated from mid-February to mid-April, while the end of the season (EOS) was concentrated from early October to mid-December. The length of growing season (LOS) ranged from 6 to 10 months. The SOS of vegetation was gradually postponed at a rate of 0.16 d·year−1. The EOS advanced at a rate of 0.69 d·year−1. The LOS was gradually shortened at a rate of 0.89 d·year−1. For each per 1000 m increase in elevation, the SOS of vegetation was postponed by 12.40 d; the EOS advanced by 0.40 d, and the LOS was shortened by 11.70 d. For the impacts of climate changes on vegetation phenology and NPP, the SOS of vegetation phenology negatively correlated with temperature but positively correlated with precipitation and NPP. The EOS and LOS positively correlated with temperature but negatively with precipitation and NPP. Results indicated that the SOS was not moved ahead but was delayed, while the EOS advanced rather than being postponed under climate change. These results can offer new insights on the phenological response to climate change in arid regions and on non-systematic changes in phenology under global warming.

Remote sensing assessment of changes of surface parameters in response to prolonged drought in the arid zone of central Iran (Gavkhoni playa)

Remotely-sensed normalized difference vegetation index (NDVI) and land surface temperature (LST) are significant indicators for evaluating the environmental consequences of climate changes in arid regions. Understanding of the relationship between these changes and land surface properties of the arid regions is important in land planning. The Gavkhoni playa is a closed basin in the arid zone of Iran that has recently undergone significant environmental changes due to decreasing precipitations. The objective of this study was to explore the spatiotemporal changes of its LST and NDVI before and after the drought event of 2014–2018. Through the application of an integrated method based on cellular fractal model and continuous wavelet transform (CWT), we investigated the relationship between variation of surface fractal dimension and distribution of LST and NDVI changes before and after the drought. The results indicated substantial changes in LST and NDVI values associated with the onset of drought conditions. Changes in the spatial distribution of LST and NDVI were particularly high in the central playa area, the western and southern sides of the playa, including the salt lake, the wetlands, and the clay flat. These areas correspond to the zone 4 of the fractal dimension map where extreme topographic anomaly and complexity. Wavelet analysis confirmed the relationship between the surface fractal dimension pattern and anomalies in LST and NDVI variations. The investigation highlighted the ability of the integrated application of the cellular fractal model and wavelet analysis to quantify the relationship between land surface properties and the spatial variation of LST and NDVI in changing environmental conditions.

EPISODIC EVENTS ON RADAR AND MULTISPECTRAL REMOTE SENSORS FROM SALAR DE AGUAS CALIENTES, CHILE

Abstract. Restricted episodic changes occurred in a short time period and over large spatial extents. Extreme weather conditions usually give rise to restricted episodic changes. Sentinel-1 radar images of the Salar de Aguas Calientes in Chile acquired in the Altiplanic winter (March 2015 and June 2017), 2018 austral winter and 2017–2018 springtime, demonstrates the ability to monitor episodic events remotely. The results of the backscattered power are encouraging and show episodic variations in VV polarization at C-band. The surface features in Salar de Aguas Calientes Sur change in response to snowfalls during either the Altiplanic or austral winter with an increase of the backscattering in presence of dry snow over the salt pan crust. Flooding events related to snow-melting during spring 2017–2018 showed a decrease in the backscattering signal over ponded water and an increase when wind blows over the water. Remote-sensing observations of the salar can provide a means for monitoring changes in the surface of the salar and a better understanding of the associated climatic episodic event processes. Furthermore, it can help to have a better understanding of environmental changes in arid regions and the understanding of global climate change.

Dust storm frequency change in relation to climate drivers

AbstractClimate variability and change in arid regions are important factors in controlling emission, frequency and movement of dust storms. This study provides robust statistical methods including univariate Mann‐Kendall block bootstrapping method and three bivariate trend assessment methods, Covariance Inversion Test, Covariance Sum Test and The Covariance Eigenvalue to detect trends in dust storm frequency across arid regions of Iran in relation to climate variability and trend in recent decades. In this regard, the annual number of dust storms from 25 stations in central arid and semi‐arid regions of Iran were selected. In addition, five major climatic variables including annual rainfall, annual maximum and average wind speed, annual maximum and average temperature were also collected. The univariate trend test indicates both increasing and decreasing trend in dust storm frequency and climate variables. The bivariate trend test shows a strong and statistically significant relationship between trend of climate variables and dust storm frequency for most of the stations across the region. Among climate variables, rainfall change has an inverse impact on dust storm frequency while wind speed and temperature have direct covariance structure with dust storm frequency. The wind speed also seems to be the most effective climate driver on dust storm frequency in arid regions of Iran, followed by temperature. The results also shows that local conditions that are not considered in this study may also play a significant role in dust storm emission in some parts of the region.

A Combination Forecasting Strategy for Precipitation, Temperature and Wind Speed in the Southeastern Margin of the Tengger Desert

Global warming is inevitably the cause of local climate change, which will have a profound impact on regional ecology, especially in the desertified steppe and steppefied desert transition zones with fragile ecological environments. In order to investigate the change trends of precipitation, temperature and wind speed for effectively realizing the restoration and protection of desert ecosystems, a combination forecasting strategy including the data pre-processing technique, sub-models selection and parameter optimization was proposed and three numerical simulation experiments based on the combination model with the weights optimized by the particle swarm optimization algorithm were designed to forecast the precipitation, temperature and wind speed in the southeastern margin of the Tengger Desert in China. Numerical results showed that the proposed combination prediction method has higher forecasting accuracy and better robustness than single neural network models and hybrid models. The proposed method is beneficial to analyze climate change in arid regions.

An Improved Conceptual Model Quantifying the Effect of Climate Change and Anthropogenic Activities on Vegetation Change in Arid Regions

Vegetation shows a greening trend on the global scale in the past decades, which has an important effect on the hydrological cycle, and thus quantitative interpretation of the causes for vegetation change is of great benefit to understanding changes in ecology, climate, and hydrology. Although the Donohue13 model, a simple conceptual model based on gas exchange theory, provides an effective tool to interpret the greening trend, it cannot be used to evaluate the impact from land use and land cover change (LULCC) on the regional scale, whose importance to vegetation change has been demonstrated in a large number of studies. Hence, we have improved the Donohue13 model by taking into account the change in vegetation cover ratio due to LULCC, and applied this model to the Yarkand Oasis in the arid region of northwest China. The estimated change trend in leaf area index (LAI) is 1.20%/year from 2001 to 2017, which accounts for approximately half of the observed (2.31%/year) by the moderate resolution imaging spectroradiometer (MODIS). Regarding the causes for vegetation greening, the contributions of: (1) LULCC; (2) atmospheric CO2 concentration; and (3) vapor pressure deficit were: (1) 88.3%; (2) 40.0%; and (3) −28.3%, respectively, which reveals that the largest contribution was from LULCC, which is probably driven by increased total water availability in whole oasis with a constant transpiration in vegetation area. The improved Donohue13 model, a simple but physics-based model, can partially explain the impact of factors related to climate change and anthropogenic activity on vegetation change in arid regions. It can be further combined with the Budyko hypothesis to establish a framework for quantifying the changes in coupled response of vegetation and hydrological processes to environment changes.

Monitoring of Land Use/Land-Cover Changes in the Arid Transboundary Middle Rio Grande Basin Using Remote Sensing

Expanding urbanization in highly fragile desert environments requires a thorough understanding of the current state and trends of land uses to achieve an optimal balance between development and the integrity of vital ecosystems. The objectives of this study are to quantify land use change over the 25-year period 1990–2015 and analyze temporal and spatial urbanization trends in the Middle Rio Grande Basin. We conclude by indicating how the results can inform on-going water resource research and public policy discussion in an arid region. Results show that the predominant upland mixed vegetation land cover category has been steadily declining, giving up land to urban and agricultural development. Urban development across the region of interest increased from just under three percent in 1990 to more than 11 percent in 2015, mainly around the major urban areas of El Paso, Ciudad Juárez, and Las Cruces. Public policy aspects related to results from this study include transfer of water rights from agriculture to land developers in cities, higher risk of flooding, loss of natural ecosystems, and increased water pollution from point and non-point sources. Various stakeholders can find the study useful for a better understanding of historical spatial and temporal aspects of urban development and environmental change in arid regions. Such insights can help municipal authorities, farmers, and other stakeholders to strike a balance between development needs and protecting vital ecosystems that support the much needed development, especially in regions that are endowed with transboundary natural resources that often are incompletely represented in single nation data.

Environmental Information Revealed by Sensitive Grain Size Component of Lake Sediments in Longcheng Yardang on the Northeast Edge of Tarim Basin

On basis of grade-standard deviation method, two sensitive grain size components (component 1:5.8∼10.0μm, component 2:60.3∼104.7μm) and a less sensitive grain size component (component 3:15.1μm∼22.9μm) were extracted from the samples of the sedimentary age of LX02 profile, which were collected from Longcheng Yardang region on the northeast edge of Tarim Basin. The study discusses the material sources and action forms of different grain size sensitive components, which can be used as an indicator to reveal the regularity of the lake and the intensity of wind-sand activity respectively. The lacustrine transgressive and regressive history of the region has been reconstructed for 72−51ka B.P. by the characteristics of the content of sensitive grain size component 2, and the palaeoclimate information of the sediments was restored, which provided the basis for exploring the distribution law of other environmental factors in lake sediments. This paper is helpful to explore the law of environmental evolution and the history of climate change in arid regions.

Agricultural Oasis Expansion and Its Impact on Oasis Landscape Patterns in the Southern Margin of Tarim Basin, Northwest China

Oasis landscape change and its pattern dynamics are considered one of the vital research areas on global land use and landscape change in arid regions. An agricultural oasis is the main site of food security and ecosystem services in arid areas. Recently, the dramatic exploitation of agricultural oases has affected oasis stability, inducing some ecological and environmental issues such as water shortage and land degradation. In this study, the Qira oasis on the southern margin of Tarim Basin, Northwest China, was selected as a study area to examine the spatiotemporal changes in an agricultural oasis and the influence on oasis landscape pattern. Based on the integration of Thematic Mapper, Enhanced Thematic Mapper Plus, and GF-1 images, the agricultural Qira oasis has rapidly increased, with annual change rates of −0.3%, 1.6%, 3.7%, and 1.5% during 1970–1990, 1990–2000, 2000–2013, and 2013–2016, respectively. With the agricultural oasis expansion, the agricultural land has increased from 91.10 km2 in 1970 to 105.04 km2 in 2016. The percentage of farmland area has increased by 15.3% in 2016 compared with that in 1970. The natural vegetation is decreasing owing to the reclamation of desert–oasis ecotone. The oasis landscape change and pattern are mainly affected by agricultural expansion under water-saving technological utilization, land use policy, and regional economic development demand. The expansion of agricultural oasis is alarming due to human overexploitation. Thus, the government should adjust the layout of agricultural development and pay considerable attention to the oasis environment sustainability. This study can provide a valuable reference on the impact of climate change and human activities on a landscape.

Monitoring and Analysing Land Use/Cover Changes in an Arid Region Based on Multi-Satellite Data: The Kashgar Region, Northwest China

In arid regions, oases ecosystems are fragile and sensitive to climate change, and water is the major limiting factor for environmental and socio-economic developments. Understanding the drivers of land use/cover change (LUCC) in arid regions is important for the development of management strategies to improve or prevent environmental deterioration and loss of natural resources. The Kashgar Region is the key research area in this study; it is a typical mountain-alluvial plain-oasis-desert ecosystem in an arid region, and is one of the largest oases in Xinjiang Uyghur Autonomous Region, China. In addition, the Kashgar Region is an important cotton and grain production area. This study’s main objectives are to quantify predominant LUCCs and identify their driving forces, based on the integration of multiple remote sensors and applications of environmental and socio-economic data. Results showed that LUCCs have been significant in the Kashgar Region during the last 42 years. Cultivated land and urban/built-up lands were the most changed land cover (LC), by 3.6% and 0.4% from 1972 to 10.2% and 3% in 2014, respectively. By contrast, water and forest areas declined. Grassland and snow-covered areas have fluctuated along with climate and human activities. Bare land was changed slightly from 1972 to 2014. According to the land use transfer matrix, cultivated land replaced grass- and forestland. Urban/built-up land mainly expanded over cultivated and bare land. LUCCs were triggered by the interplay of natural and social drivers. Increasing runoff, caused by regional climate changes in seasonal variation, and snow melt water, have provided water resources for LC changes. In the same way, population growth, changes in land tenure, and socio-economic development also induced LUCCs. However, expansion of cultivated land and urban/built-up land led to increased water consumption and stressed fragile water systems during on-going climate changes. Therefore, the selection of adaption strategies relating to climate change and oasis development is very important for sustainable development in the Kashgar Region.

Respuesta hidrológica al cambio climático en regiones áridas: caso de estudio en los Comondú, Baja California Sur, México

Respuesta hidrológica al cambio climático en regiones áridas: caso de estudio en los Comondú, Baja California Sur, México

Quantitative Trend, Sensitivity and Contribution Analyses of Reference Evapotranspiration in some Arid Environments under Climate Change

The temporal trend of reference crop evapotranspiration (ET0) and contribution of associated meteorological factors to the ET0 trend were assessed for 17 arid areas. Sensitivity of ET0 to changes in key meteorological variables was also analyzed. To study temporal trend of ET0, Mann-Kendall trend test was employed. Quantitative contribution and sensitivity analyses were carried out, respectively, using a dimensionless relative sensitivity coefficient and detrending method. Results indicated that ET0 has an increasing trend in 70.6, 64.7, 70.6, 76.5 and 70.0%, of sites respectively, in winter, spring, summer, autumn and entire year. This positive trend was significant (p ≤ 0.05) in 47.0, 35.3, 35.3, 29.4 and 35.3% of sites, respectively, for the same seasons. There was a significant change-point in winter, spring, summer, autumn and annual ET0 series at 64.7, 52.9, 64.7, 64.7 and 82.3% of stations, respectively. In 35.3 and 35.3% of sites, solar radiation and wind speed were the most sensitive climatic factors on ET0, respectively. ET0 exhibited the highest sensitivity to the relative humidity changes in coastal sites. Changes of wind speed contributed much more than other factors to the annual ET0 trend in 58.8% of investigated sites. The negative trend in wind speed nearly nullified the positive effects of increased air temperature on ET0 over 1966–2012 in 23.5% of stations. Changes in ET0 were attributed to wind speed changes in most locations. Given the upward trend of ET0 in the majority of locations, proper water management is required to avoid negative impacts of climate change in arid regions.

The application of polynomial analyses to detect global vegetation dynamics during 1982–2012

ABSTRACTUse of the normalized difference vegetation index (NDVI) to build long-term vegetation trends is one of the most effective techniques for identifying global environmental change. Trend identification can be achieved by ordinary least squares (OLS) analysis or the Theil–Sen (TS) procedure with a Mann–Kendall (MK) significance test, and these linear regression approaches have been widely used. However, vegetation changes are not linear, and thus the response of vegetation to global climate change may follow non-linear trends. In this article, a polynomial trend-fitting method, which uses stepwise regression and expands on previous research, is presented. With an improved fitting ability, this procedure may reveal trends that were concealed by linear fitting methods. Globally, the traditional TS-MK method reveals significant greening trends for 37.27% of vegetated land, and significant browning trends for 7.98%. Using the polynomial analysis, 34.62% of pixels were fitted by high-order trends. The significant greening trends covered up to 30% of cultivated land, thus indicating that cultivated vegetation may be increasing faster than natural vegetation. Significant vegetation browning mostly occurred in sparse vegetation areas, which suggests that vegetation growth may be more sensitive to climate change in arid regions. Our results show that use of polynomial analysis can help further elucidate global NDVI trends.

Adaptation of the agricultural sector to the effects of climate change in arid regions: competitive advantage date palm cropping patterns under water scarcity conditions

This research paper highlights the adverse effects of climate change on the agricultural sector in Saudi Arabia and the actions taken to adapt to these adverse effects. Special focus was given to the potential to optimise the reallocation of scarce water resources among the competitive advantage date palm cropping regions in Saudi Arabia using a mathematical sector modelling approach. The results showed great potential for Saudi Arabia to adapt to the adverse effects of climate change by optimising the date palm cropping pattern in accordance with its scarce water resources and limited cultivated lands. The optimised scenario would result in a high net annual return, equivalent to about 881.76 million US$ year−1, and an increase on the water use return from about 0.97 US$ cm−1 in the base year to approximately 1.31 US$ cm−1. The optimised scenario would also provide the opportunity to reduce the allocated date palm cropping area by approximately 4% (from approximately 118,250 hectares to approximately 113,446 hectares) and to reduce the water demand by approximately 1% (from 681.06 million cubic metres (MCM) per year to approximately 674.28 MCM per year).

A framework for the assessment of reservoir operation adaptation to climate change in an arid region

It is essential to assess the adaptation of reservoir operation to climate change in arid regions. The main objective of this research is to propose a framework for assessment of reservoir rule-curve (RRC) adaptation for climate change scenarios. The framework is applied to an arid zone in Iran and consists of the three models: downscaling, rainfall-runoff and reservoir optimisation models. LARS-WG is tested in 99% confidence level before to using it as downscaling model. Seven artificial neural network models are proposed, examined and compared with IHACRES to find proper rainfall-runoff model for arid zone. Current and adapted reservoir rule curves are derived by dynamic programming optimisation. The results demonstrate capability of proposed framework in assessment of adaptation and show that global warming negatively influences proposed index (water supply index) in normal and wet years, but has positive influence for dry years. It also improves reservoir reliability, but it cannot restore current reliability.

OSL dating of the Miam Qanat (KĀRIZ) system in NE Iran

This article presents the first direct absolute dating method of a Qanat system obtained through optically stimulated luminescence (OSL) dating of grains in spoil heaps, using feldspar single-grain, feldspar multi-grain and quartz multi-grain samples. This novel and highly promising approach to improving our understanding of the chronology of Qanats is more important than the final age results.Hitherto, dating of Qanats has been based on indirect evidence from historical reports or archaeological investigations of nearby settlements. This study demonstrate the ability of OSL to date this type of subterranean irrigation feature, which is important in the study of both the archaeology of human settlement and palaeoenvironmental change in arid regions. This method can also be used for dating wells and handmade ditches and canals.Our results show that advanced irrigation technologies existed at Miam in what is now north-east Iran much earlier than previously thought. Dating the now disused Qanat at 3.6–4.3 ka makes it the oldest known. Single-grain dating of sand-sized feldspar that overlie construction spoil show that the Miam Qanat was maintained until at least 1.6 ka. The early development of Qanat irrigation indicates that the causes of widespread societal collapse in eastern Iran in the Bronze Age might not have been driven purely by climatic pressures.

Luminescence dating of irrigation systems: Application to a qanat in Aragón, Spain

Optically stimulated luminescence (OSL) techniques have been applied to investigate the potential for dating the deposition of upcast mounds associated with qanat ventilation shafts at the site of a medieval qanat located in Aragón, Spain. Coarse quartz grains, extracted from sediment samples taken from excavated sections of several mounds, possessed sufficiently strong OSL to enable an evaluation of equivalent dose by applying the single aliquot regenerative procedure to small aliquots, each containing an individual bright grain. The OSL dates for both palaeosol and overlying upcast indicate that a chronostratigraphic record has been preserved within the mounds investigated, and micromorphological analysis of thin sections of sediment blocks taken from the mounds is shown to provide an essential means of verifying the characteristics of the strata, in particular, the critical interface of upcast and the ancient ground surface. The earliest OSL dates for basal deposits taken from two separate sections of the same mound are in agreement, placing the mound construction during the first half of the 13th century A.D. However, in two other mounds the OSL dates for the deposition of upcast are internally consistent with the stratigraphy but significantly later, dating to the 16th and 17th centuries A.D. We interpret the differences between the dates for the upcast deposition to be the result of partial erosion of the upper shaft and later repair of the mounds, and this finding underlines the importance of both examining multiple mounds in the same qanat system and the internal structure of each sampled mound. This exploratory work demonstrates the potential for wider application of OSL for dating this important type of subterranean irrigation feature in the study of both the archaeology of human settlement and palaeoenvironmental change in arid regions.

Long‐term vegetation dynamics (40 yr) in the Succulent Karoo, South Africa: effects of rainfall and grazing

AbstractQuestionsVegetation change in arid regions with a coefficient of rainfall exceeding 33% usually displays non‐equilibrium dynamics, where abiotic factors override internal biotic controls. Irreversible changes have nonetheless also been described for arid regions. What are the contributions of internal/equilibrium vs external/non‐equilibrium factors to vegetation dynamics and can degradation due to overstocking be reversed after removal of livestock?LocationGoegap Nature Reserve, Namaqualand, South Africa.MethodsThe descending point method was conducted annually from 1974 at two transects. Vegetation change was assessed in terms of vegetation cover, species composition, life‐form composition, range condition, species richness and diversity. Principal coordinates analysis was used to illustrate the trajectories in floristic data, and the effects of stocking density and rainfall were examined with redundancy analysis.ResultsVegetation cover, species richness and Shannon‐Wiener index of diversity showed an increase and range condition improved with time. These positive changes could be related to the removal of high numbers of livestock and low wildlife numbers in the first years of survey. A gradual decline in the rate of increase in some of these parameters could be related to high grazing pressure during the later monitored years. There was a notable increase in non‐succulent chamaephytes, but the initial increase in succulent chamaephytes was not sustained. The directional change evident in perennial species composition, supports the equilibrium concept, whereby the negative changes induced by heavy grazing were partially reversed. Within the directional change, four quasi‐stable states could be distinguished, which could be reconciled with the state‐and‐transition model. The annual component showed no directional change, but displayed event‐driven, non‐equilibrium dynamics by fluctuating in reaction to the timing and quantity of rainfall.ConclusionsThe vegetation change displayed elements of both equilibrium and non‐equilibrium dynamics, and demonstrated that the effects of heavy grazing in the Succulent Karoo were reversible. Overall, the recovery process proceeded slowly and was primarily detected in the perennial component of the vegetation. The increase in wildlife numbers in the later studied years and decline in perennial vegetation cover stress the need for active management of animal numbers to avoid vegetation degradation.

Testing the applicability of vacuum-encapsulated 40Ar/39Ar geochronology to pedogenic palygorskite and sepiolite

The difficulty of isolating intact, mineralogically pure pedogenic crystals from cemented soil is one of the most significant obstacles to quantifying rates of soil formation, geomorphic processes, and climate change in arid regions. We evaluate the applicability of vacuum encapsulated 40Ar/39Ar geochronology to pedogenic palygorskite and sepiolite extracted from the 4 to 5 Ma, extant Mormon Mesa petrocalcic soil-geomorphic surface of southern Nevada, and from the 780 ka to 2 Ma Jornada Experimental Range La Mesa soil-geomorphic surface near Las Cruces, New Mexico. Selective dissolution of cements using NaOAc and Tiron, accompanied by particle size fractionation, was used to isolate the pedogenic Mg-phyllosilicates. Scanning electron microscopy, inductively-coupled plasma spectrometry, X-ray diffraction, gas chromatograph mass spectrometry, and Ar isotope analysis were used to determine whether extraction impacted palygorskite/sepiolite suitability for 40Ar/39Ar geochronology. We found no adverse morphological or mineralogical effects, but meaningful ages could not be obtained due to small amounts of old, detrital phyllosilicates in the samples. While the potential of pedogenic palygorskite and/or sepiolite for geochronology now seems limited, results from this study may prove relevant for samples from other, non-pedogenic surface environments. It is hoped that this work will encourage further research towards successful 40Ar/39Ar geochronology of pedogenic phyllosilicates, as well as inform future geochemical or isotopic studies of individual pedogenic mineral species.

Magnetic properties of surface soils in the Chinese Loess Plateau and the adjacent Gobi areas, and their implication for climatic studies

Sixty-two surface soil samples, collected along a precipitation gradient in the Loess Plateau and the Alxa Plateau area, northwest China, were analyzed using environmental magnetic parameters (χlf, χfd%, χARM, SIRM, HIRM, SOFT, and back field IRM), grain size, and weight loss on ignition. The results show that the magnetic mineral assemblage in the surface soil is dominated by magnetite and maghemite, with some hematite. Cross plots of χfd% vs. χARM/SIRM indicate that the main magnetic grain sizes in the surface soils are pseudo single domain (PSD) and multidomain (MD). The samples from the Alxa area are dominated by magnetic minerals with a larger grain size while those from the Loess Plateau are dominated by magnetic minerals with a finer grain size. The main magnetic minerals in the surface soil of the Loess Plateau originate from both the aeolian dust and pedogenic processes, with the later dominating. Compared to magnetic susceptibility, frequency-dependent magnetic susceptibility has a stronger correlation with precipitation in this large area of complex geology and topography. This result is not consistent with previous studies and we suggest that caution is needed when using magnetic susceptibility as an indicator of environmental change in arid regions.