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Several recommendations have been proposed for detecting land use and land cover change (LULCC) on the environment from, observed climatic records and to modeling to improve its understanding and its impacts on climate. Researchers need to detect LULCCs accurately at appropriate scales within a specified time period to better understand their impacts on climate and provide improved estimates of future climate. The US Climate Reference Network (USCRN) can be helpful in monitoring impacts of LULCC on near-surface atmospheric conditions, including temperature. The USCRN measures temperature, precipitation, solar radiation, and ground or skin temperature. It is recommended that the National Climatic Data Center (NCDC) and other climate monitoring agencies develop plans and seek funds to address any monitoring biases that are identified and for which detailed analyses have not been completed.

In Part I of this observational study inquiring into the relative influences of “top down” synoptic atmospheric conditions and “bottom up” land surface mesoscale conditions in deep convection for the humid lowlands of the Midwest U.S. Central Corn Belt (CCB), the composite atmospheric environments for afternoon and evening periods of convection (CV) versus no convection (NC) were determined for two recent summers (1999 and 2000) having contrasting precipitation patterns and amounts. A close spatial correspondence was noted between composite synoptic features representing baroclinity and upward vertical motion with the observed precipitation on CV days when the “background” (i.e., free atmosphere) wind speed exceeded approximately 10 m s−1 at 500 hPa (i.e., “stronger flow”). However, on CV days when wind speeds were For the 1999 and 2000 summers (item 1 above), thermodynamic composites determined for V(500) categories having minimal differences in synoptic meteorological fields on CV minus NC (CV − NC) days (i.e., weaker flow), show statistically significant increases in atmospheric moisture (e.g., greater precipitable water; lower LCL and LFC) and static instability [e.g., positive convective available potential energy (CAPE)] compared to NC days. Moreover, CV days for both weaker and stronger background flow have associated subregional-scale thermodynamic patterns indicating free convection at the earth’s surface, supported by a synoptic pattern of at least weakly upward motion of air in the midtroposphere in contrast to NC days. The possibility that aerodynamic contrasts along QPVBs readily permit air to be lofted above the LFC when the lower atmosphere is moist, thereby assisting or enhancing deep convection on CV days, is supported by the multiyear analysis (item 2 above). In early summer when LULC boundaries are most evident, precipitation on weaker flow days is significantly greater within 20 km of boundaries than farther away, but there is no statistical difference on stronger flow days. Statistical relationships between boundary mean attributes and mean precipitation change sign between early summer (positive) and late summer (negative), in accord with shifts in the satellite-retrieved maximum radiances from forest to crop areas. These phenological changes appear related, primarily, to contrasting soil moisture and implied evapotranspiration differences. Incorporating LULC boundary locations and phenological status into reliable forecast fields of lower-to-midtropospheric humidity and wind speed should lead to improved short-term predictions of convective precipitation in the Corn Belt and also, potentially, better climate seasonal forecasts.

In the Midwest U.S. Corn Belt, the 1999 and 2000 summer seasons (15 June–15 September) expressed contrasting spatial patterns and magnitudes of precipitation (1999: dry; 2000: normal to moist). Distinct from the numerical modeling approach often used in studies of land surface–climate interactions, a “synoptic climatological” (i.e., stratified composite) approach is applied to observation data (e.g., precipitation, radar, and atmospheric reanalyses) to determine the relative influences of “top-down” synoptic atmospheric circulation (Part I, this paper) and “bottom-up” land surface mesoscale conditions (Part II) on the predominantly convective precipitation variations. Because mesoscale modeling suggests that the free-atmosphere wind speed (“background wind”) regulates the land surface–atmosphere mesoscale interaction, each day’s spatial range of wind speed at 500 hPa [V(500)] over the Central Corn Belt (CCB) is classified into one of five categories ranging from “weak flow” to “jet maximum.” Deep convective activity (i.e., presence/absence and morphological signature type) is determined for each afternoon and early evening period from the Next Generation Weather Radar (NEXRAD) imagery. Frequencies of the resulting background wind–convection joint occurrence types for the 1999 and 2000 summer seasons are examined in the context of the statistics determined for summers in the longer period of 1996–2001, and also compose categories for which NCEP–NCAR reanalysis (NNR) fields are averaged to yield synoptic composite environments for the two study seasons. The latter composites are compared visually with high-resolution (spatial) composites of precipitation to help identify the influence of top-down climate controls. The analysis confirms that reduced (increased) organization of radar-indicated deep convection tends to occur with weaker (stronger) background flow. The summers of 1999 and 2000 differ from one another in terms of background flow and convective activity, but more so with respect to the six-summer averages, indicating that a fuller explanation of the precipitation differences in the two summers must be sought in the analysis of additional synoptic meteorological variables. The composite synoptic conditions on convection (CV) days (no convection (NC) days) in 1999 and 2000 are generalized as follows: low pressure incoming from the west (high pressure or ridging), southerly (northerly) lower-tropospheric winds, positive (negative) anomalies of moisture in the lower troposphere, rising (sinking) air in the midtroposphere, and a location south of the upper-tropospheric jet maximum (absence of an upper-tropospheric jet or one located just south of the area). Features resembling the “northerly low-level jets” identified in previous studies for the Great Plains are present on some NC-day composites. On CV days the spatial synchronization of synoptic features implying baroclinity increases with increasing background wind speed. The CV and NC composites differ least on days of weaker flow, and there are small areas within the CCB having no obvious association between precipitation elevated amounts and synoptic circulation features favoring the upward motion of air. These spatial incongruities imply a contributory influence of “stationary” (i.e., climatic) land surface mesoscale processes in convective activity, which are examined in Part II.

Summer simulations over the contiguous United States and Mexico with the Regional Atmospheric Modeling System (RAMS) dynamically downscaling the NCEP–NCAR Reanalysis I for the period 1950–2002 (described in Part I of the study) are evaluated with respect to the three dominant modes of global SST. Two of these modes are associated with the statistically significant, naturally occurring interannual and interdecadal variability in the Pacific. The remaining mode corresponds to the recent warming of tropical sea surface temperatures. Time-evolving teleconnections associated with Pacific SSTs delay or accelerate the evolution of the North American monsoon. At the period of maximum teleconnectivity in late June and early July, there is an opposite relationship between precipitation in the core monsoon region and the central United States. Use of a regional climate model (RCM) is essential to capture this variability because of its representation of the diurnal cycle of convective rainfall. The RCM also captures the observed long-term changes in Mexican summer rainfall and suggests that these changes are due in part to the recent increase in eastern Pacific SST off the Mexican coast. To establish the physical linkage to remote SST forcing, additional RAMS seasonal weather prediction mode simulations were performed and these results are briefly discussed. In order for RCMs to be successful in a seasonal weather prediction mode for the summer season, it is required that the GCM provide a reasonable representation of the teleconnections and have a climatology that is comparable to a global atmospheric reanalysis.

This paper discusses the diverse climate forcings that impact agricultural systems, and contrasts the current paradigm of using global models downscaled to agricultural areas (a top-down approach) with a new paradigm that first assesses the vulnerability of agricultural activities to the spectrum of environmental risk including climate (a bottom-up approach). To illustrate the wide spectrum of climate forcings, regional climate forcings are presented including land-use/land-cover change and the influence of aerosols on radiative and biogeochemical fluxes and cloud/precipitation processes, as well as how these effects can be teleconnected globally. Examples are presented of the vulnerability perspective, along with a small survey of the perceived drought impacts in a local area, in which a wide range of impacts for the same precipitation deficits are found. This example illustrates why agricultural assessments of risk to climate change and variability and of other environmental risks should start with a bottom-up perspective.

A storm-resolving version of the Regional Atmospheric Modeling System is executed over St. Louis, Missouri, on 8 June 1999, along with sophisticated boundary conditions, to simulate the urban atmosphere and its role in deep, moist convection. In particular, surface-driven low-level convergence mechanisms are investigated. Sensitivity experiments show that the urban heat island (UHI) plays the largest role in initiating deep, moist convection downwind of the city. Surface convergence is enhanced on the leeward side of the city. Increased momentum drag over the city induces convergence on the windward side of the city, but this convergence is not strong enough to initiate storms. The nonlinear interaction of urban momentum drag and the UHI causes downwind convection to erupt later, because momentum drag over the city regulates the strength of the UHI. In all simulations including a UHI, precipitation totals are enhanced downwind of St. Louis. Topography around St. Louis also affects storm development. There is a large sensitivity of simulated urban-enhanced convection to the details of the urban surface model.

In this study, the combined effect of the Atlantic Multidecadal Oscillation (AMO) and El Nino Southern Oscillation (ENSO) on the Lake Chad (LC) level variability is explored. Our results show that the lake level at the Bol monitoring station has a statistically significant correlation with precipitation (R2 = 0.6, at the 99.5% confidence level). The period between the late 1960s and early 1970s marked a turning point in the response of the regional rainfall to climatic drivers, thereby severely affecting the LC level. Our results also suggest that the negative impact of the cold phase of AMO on Sahel precipitation masks and supersedes the positive effect of La Nina in the early the 1970s. The drop in the size of LC level from 282.5 m in the early 1960s to about 278.1 m in 1983/1984 was the largest to occur within the period of study (1900–2010) and coincides with the combined cold phase of AMO and strong El Nino phase of ENSO. Further analyses show that the current warm phase of AMO and increasing...

The United States Midwest over the last two decades has experienced marked warm season climate anomalies, including droughts and major floods. While the development of these extreme events can usually be traced to anomalies in atmospheric circulation, and may include teleconnections, studies based on model simulations have shown that land surface forcing may be partly responsible for the persistence of these climate anomalies. This study evaluates the presence and strength of long-term land surface-climate interactions in the U.S. Midwest. We do this via an analysis of the cross-seasonal (spring and summer) associations between temperature and moisture (Palmer Drought Severity Index-PDSI, Crop Moisture-Z Index, and precipitation) anomalies. Direct and lag correlations for the 1895–1995 and 1948–1995 periods show that warm and dry summers tend to follow warm spring seasons. These results imply that springtime precipitation anomalies may help to determine the temperature regime of the following summer, possibly via the moisture content of the upper soil. We also show that broad land cover types tend to modulate summer climate anomalies in the U. S. Midwest.

Land-use and land-cover changes (LULCC) significantly affect weather and climate as iswell documented in the scientific literature. These impacts include changes in air temperature, precipitation, atmospheric moisture content, energy fluxes, and mesoscale and potentially large-scale circulations. Recently, the United States National Research Council (2005) highlighted the importance of LULCC and recommended the broadening of the climate-change issue to include land-use/land-cover processes as an important climate forcing. The report noted that, “Regional variations in radiative forcing may have important regional and global climatic implications that are not resolved by the concept of global mean radiative forcing. Tropospheric aerosols and landscape changes have particularly heterogeneous forcings. To date, there have been only limited studies of regional radiative forcing and response. Indeed, it is not clear how best to diagnose a regional forcing and response in the observational record; regional forcings can lead to global climate responses, while global forcings can be associated with regional climate responses. Regional diabatic heating can also cause atmospheric teleconnections that influence regional climate thousands of kilometres away from the point of forcing. Improving societally relevant projections of regional climate impacts will require a better understanding of the magnitudes of regional forcings and the associated climate responses.” Therefore, it is critical that we further investigate and understand the impacts of LULCC on weather and climate predictability. In this context, an National Science Foundation (NSF) funded workshop was organized in Boulder, Colorado, USA in 2007 to further highlight the importance of LULCC, to present results of new research in LULCC, and to discuss the challenges of the monitoring and modelling of LULCC at various temporal and spatial scales. The articles included in this