Analysing the distance decay of community similarity in river networks using Bayesian methods

The distance decay of community similarity (DDCS) is a pattern that is widely observed in terrestrial and aquatic environments. Niche-based theories argue that species are sorted in space according to their ability to adapt to new environmental conditions. The ecological neutral theory argues that community similarity decays due to ecological drift. The continuum hypothesis provides an intermediate perspective between niche-based theories and the neutral theory, arguing that niche and neutral factors are at the opposite ends of a continuum that ranges from competitive to stochastic exclusion. We assessed the association between niche-based and neutral factors and changes in community similarity measured by Sorensen’s index in riparian plant communities. We assessed the importance of neutral processes using network distances and flow connection and of niche-based processes using Strahler order differences and precipitation differences. We used a hierarchical Bayesian approach to determine which perspective is best supported by the results. We used dataset composed of 338 vegetation censuses from eleven river basins in continental Portugal. We observed that changes in Sorensen indices were associated with network distance, flow connection, Strahler order difference and precipitation difference but to different degrees. The results suggest that community similarity changes are associated with environmental and neutral factors, supporting the continuum hypothesis.

Spatial and temporal analysis of Iran precipitation

In this study, spatial and temporal analysis of precipitation in Iran in 2019 and 2020 has been studied. The average annual precipitation in 2019 is about 345 mm and in 2020 285 mm. In 2019, the maximum precipitation was in the western and northwestern regions, and the minimum precipitation was in the central and eastern regions. In 2020, the maximum precipitation was in the northwestern areas and the minimum precipitation was in the central, eastern and southwestern areas. Northwestern regions of Iran have a positive precipitation difference, i.e. in 2020 it had more precipitation. The southern and western regions have a negative difference, i.e. in 2020, there was less rain.

Spatial and temporal analysis of Iran precipitation

In this study, spatial and temporal analysis of precipitation in Iran in 2019 and 2020 has been studied. The average annual precipitation in 2019 is about 345 mm and in 2020 285 mm. In 2019, the maximum precipitation was in the western and northwestern regions, and the minimum precipitation was in the central and eastern regions. In 2020, the maximum precipitation was in the northwestern areas and the minimum precipitation was in the central, eastern and southwestern areas. Northwestern regions of Iran have a positive precipitation difference, i.e. in 2020 it had more precipitation. The southern and western regions have a negative difference, i.e. in 2020, there was less rain.

The Multidecadal Variability of the Asymmetric Mode of the Boreal Autumn Hadley Circulation and Its Link to the Atlantic Multidecadal Oscillation

Previous studies show that the first principal mode of the variability of the seasonal mean Hadley circulation (HC) is an equatorial asymmetric mode (AM) with long-term trend. This study demonstrates that the variability of the boreal autumn [September–November (SON)] HC is also dominated by an AM, but with multidecadal variability. The SON AM has ascending and descending branches located at approximately 20°N and 20°S, respectively, and explains about 40% of the total variance. Further analysis reveals that the AM is closely linked to the Atlantic multidecadal oscillation (AMO), which is associated with a large cross-equatorial sea surface temperature (SST) gradient and sea level pressure (SLP) gradient. The cross-equatorial thermal contrast further induces an equatorial asymmetric HC anomaly. Numerical simulations conducted on an atmospheric general circulation model also suggest that AMO-associated SST anomalies can also induce a cross-equatorial SLP gradient and anomalous vertical shear of the meridional wind at the equator, both of which indicate asymmetric HC anomaly. Therefore, the AM of the variability of the boreal autumn HC has close links to the AMO. Further analysis demonstrates that the AMO in SON has a closer relationship with AM than those in the other seasons. A possible reason is that the AMO-associated zonal mean SST anomaly in the tropics has differences among the four seasons, which leads to different atmospheric circulation responses. The AM in SON has inversed impacts on the tropical precipitation, suggesting that the precipitation difference between the northern and southern tropics has multidecadal variability.

Actual evapotranspiration and precipitation measured by lysimeters: a comparison with eddy covariance and tipping bucket

This study compares actual evapotranspiration (ETa) measurements by a set of six weighable lysimeters, ETa estimates obtained with the eddy covariance (EC) method, and evapotranspiration calculated with the full-form Penman–Monteith equation (ETPM) for the Rollesbroich site in the Eifel (western Germany). The comparison of ETa measured by EC (including correction of the energy balance deficit) and by lysimeters is rarely reported in the literature and allows more insight into the performance of both methods. An evaluation of ETa for the two methods for the year 2012 shows a good agreement with a total difference of 3.8% (19 mm) between the ETa estimates. The highest agreement and smallest relative differences (< 8%) on a monthly basis between both methods are found in summer. ETa was close to ETPM, indicating that ET was energy limited and not limited by water availability. ETa differences between lysimeter and EC were mainly related to differences in grass height caused by harvest and the EC footprint. The lysimeter data were also used to estimate precipitation amounts in combination with a filter algorithm for the high-precision lysimeters recently introduced by Peters et al. (2014). The estimated precipitation amounts from the lysimeter data differ significantly from precipitation amounts recorded with a standard rain gauge at the Rollesbroich test site. For the complete year 2012 the lysimeter records show a 16 % higher precipitation amount than the tipping bucket. After a correction of the tipping bucket measurements by the method of Richter (1995) this amount was reduced to 3%. With the help of an on-site camera the precipitation measurements of the lysimeters were analyzed in more detail. It was found that the lysimeters record more precipitation than the tipping bucket, in part related to the detection of rime and dew, which contribute 17% to the yearly difference between both methods. In addition, fog and drizzle explain an additional 5.5% of the total difference. Larger differences are also recorded for snow and sleet situations. During snowfall, the tipping bucket device underestimated precipitation severely, and these situations contributed also 7.9% to the total difference. However, 36% of the total yearly difference was associated with snow cover without apparent snowfall, and under these conditions snow bridges and snow drift seem to explain the strong overestimation of precipitation by the lysimeter. The remaining precipitation difference (about 33%) could not be explained and did not show a clear relation to wind speed. The variation of the individual lysimeters devices compared to the lysimeter mean are small, showing variations up to 3% for precipitation and 8% for evapotranspiration.

Actual evapotranspiration and precipitation measured by lysimeters: a comparison with eddy covariance and tipping bucket

This study compares actual evapotranspiration (ETa) measurements by a set of six weighable lysimeters, ETa estimates obtained with the eddy covariance (EC) method, and potential crop evapotranspiration according to FAO (ETc-FAO) for the Rollesbroich site in the Eifel (Western Germany). The comparison of ETa measured by EC (including correction of the energy balance deficit) and by lysimeters is rarely reported in literature and allows more insight into the performance of both methods. An evaluation of ETa for the two methods for the year 2012 shows a good agreement with a total difference of 3.8% (19 mm) between the ETa estimates. The highest agreement and smallest relative differences (<8%) on monthly basis between both methods are found in summer. ETa was close to ETc-FAO, indicating that ET was energy limited and not limited by water availability. ETa differences between lysimeter, ETc-FAO, and EC were mainly related to differences in grass height caused by harvesting management and the EC footprint. The lysimeter data were also used to estimate precipitation amounts in combination with a filter algorithm for high precision lysimeters recently introduced by Peters et al. (2014). The estimated precipitation amounts from the lysimeter data show significant differences compared to the precipitation amounts recorded with a standard rain gauge at the Rollesbroich test site. For the complete year 2012 the lysimeter records show a 16% higher precipitation amount than the tipping bucket. With the help of an on-site camera the precipitation measurements of the lysimeters were analyzed in more detail. It was found that the lysimeters record more precipitation than the tipping bucket in part related to the detection of rime and dew, which contributes 17% to the yearly difference between both methods. In addition, fog and drizzle explain an additional 5.5% of the total difference. Larger differences are also recorded for snow and sleet situations. During snowfall, the tipping bucket device underestimated precipitation severely and these situations contributed also 7.9% to the total difference. However, 36% of the total yearly difference was associated to snow cover without apparent snowfall and under these conditions snow bridges and snow drift seem to explain the strong underestimation of precipitation by the lysimeter. The remaining precipitation difference (about 33%) could not be explained, and did not show a clear relation with wind speed. The variations of the individual lysimeters devices compared to the lysimeter mean of 2012 are small showing variations up to 3% for precipitation and 8% for evapotranspiration.

Sensitivity of boreal-summer circulation and precipitation to atmospheric aerosols in selected regions – Part 1: Africa and India

Version-4 of the Goddard Earth Observing System (GEOS-4) General Circulation Model (GCM) was employed to assess the influence of potential changes in aerosols on the regional circulation, ambient temperatures, and precipitation in four selected regions: India and Africa (current paper), as well as North and South America (companion paper). Ensemble-simulations were carried out with the GCM to assess the aerosol direct and indirect effects, hereafter ADE and AIE. Each simulation was started from the NCEP-analyzed initial conditions for 1 May and was integrated through May-June-July-August of each year: 1982–1987 to provide an ensemble set of six simulations. In the first set, called experiment (#1), climatological aerosols were prescribed. The next two experiments (#2 and #3) had two sets of simulations each: one with 2X and other with 1/2X the climatological aerosols over each of the four selected regions. In experiment #2, the anomaly regions were advectively restricted (AR), i.e., the large-scale prognostic fields outside the aerosol anomaly regions were prescribed while in experiment #3, the anomaly regions were advectively Interactive (AI) as is the case in a normal GCM integrations, but with the same aerosols anomalies as in experiment #2. Intercomparisons of circulation, diabatic heating, and precipitation difference fields showed large disparities among the AR and AI simulations, which raised serious questions about the proverbial AR assumption, commonly invoked in regional climate simulation studies. Consequently AI simulation mode was chosen for the subsequent studies. Two more experiments (#4 and #5) were performed in the AI mode in which ADE and AIE were activated one at a time. The results showed that ADE and AIE work in concert to make the joint influences larger than sum of each acting alone. Moreover, the ADE and AIE influences were vastly different for the Indian and Africa regions, which suggest an imperative need to include them rationally in climate models. We also found that the aerosol induced increase of tropical cirrus clouds would potentially offset any cirrus thinning that may occur due to warming in response to CO2 increase.

Testing of new cultivars of perennial grasses in year of sowing

Testing of new cultivars of perennial grasses cocksfoot (Dactylis glomerata L.), meadow fescue (Festuca pratensis L.) and tall fescue (Festuca arundinacea Huds.) was carried out on experimental field of the Institute for Animal Husbandry in year 2005. Trial was set according to random block system, on 10m2, soil type carbonate chernozem. Climatic conditions in year of sowing were at the level of average values for several years for daily temperature, 12,40C compared to 12,10C, and for precipitation difference was even greater 831,6mm compared to average calculated for several years of 645,2mm. Main morphological and phenological traits of plants were investigated, plant growth, height at 1st cut, plant regeneration after 10 days, as well as production of green mass and dry matter. All five cocksfoot cultivars had considerably higher yields per cuts, total (2,12-2,69 t ha-1). Two cultivars of meadow fescue showed no significant difference in yield of dry matter (1,84-2,03 t ha-1), whereas cultivars of tall fescue differed highly significantly in this regard (1,84-1,62 t ha-1). Also, main parameters of plant quality, organic matter, content of crude protein, crude fibre and crude fat in the 2nd cut were determined. Investigated cultivars of cocksfoot and tall fescue differed significantly, whereas cultivars of meadow fescue were very similar. Obtained results were processed using variation statistical methods and mean values were tested using LSD test.