Modelling water temperature in TOXSWA

A reasonably accurate estimate of the water temperature is necessary for a good description of the degradation of plant protection products in water which is used in the surface water model TOXSWA. Based on a consideration of basic physical processes that describe the influence of weather on the energy balance of natural water bodies, we propose to extend TOXSWA with a 1D bulk approach to estimate water temperature. Evaluation of such a system confirmed that it is physically realistic and yet simple, with limited data requirements. It is expected to perform reasonably well in most conditions, and fits well into the present structure of the TOXSWA model. In particular the estimation of degradation rates in shallow and turbid water will benefit from introducing the proposed system

Diagnosis of Local Land-Atmosphere Feedbacks in India

Following the convective triggering potential (CTP)–humidity index (HIlow) framework by Findell and Eltahir, the sensitivity of atmospheric convection to soil moisture conditions is studied for India. Using the same slab model as Findell and Eltahir, atmospheric conditions in which the land surface state affects convective precipitation are determined. For India, CTP–HIlow thresholds for land surface–atmosphere feedbacks are shown to be slightly different than for the United States. Using atmospheric sounding data from 1975 to 2009, the seasonal and spatial variations in feedback strength have been assessed. The patterns of feedback strengths thus obtained have been analyzed in relation to the monsoon timing. During the monsoon season, atmospheric conditions where soil moisture positively influences precipitation are present about 25% of the time. During onset and retreat of the monsoon, the south and east of India show more potential for feedbacks than the north. These feedbacks suggest that large-scale irrigation in the south and east may increase local precipitation. To test this, precipitation data (from 1960 to 2004) for the period about three weeks just before the monsoon onset date have been studied. A positive trend in the precipitation just before the monsoon onset is found for irrigated stations. It is shown that for irrigated stations, the trend in the precipitation just before the monsoon onset is positive for the period 1960–2004. For nonirrigated stations, there is no such upward trend in this period. The precipitation trend for irrigated areas might be due to a positive trend in the extent of irrigated areas, with land–atmosphere feedbacks inducing increased precipitation

SWAP Version 3.2. Theory description and user manual

SWAP 3.2 simulates transport of water, solutes and heat in the vadose zone. It describes a domain from the top of canopy into the groundwater which may be in interaction with a surface water system. The program has been developed by Alterra and Wageningen University, and is designed to simulate transport processes at field scale and during whole growing seasons. This is a new release with special emphasis on numerical stability, macro pore flow, and options for detailed meteorological input and linkage to other models. This manual describes the theoretical background, model use, input requirements and output tables

Direct impact of atmospheric CO2 enrichment on regional transpiration

Plant physiological research has revealed that stomatal aperture of many plant species is reduced by CO 2 . Therefore, the question has been raised as to how transpiration will be affected if the ambient C0 2 concentration increases. This study focuses on the prediction of changes in transpiration at the regional scale (10-100 km horizontal, 1-5 km vertical). A rather detailed, coupled vegetation- Planetary Boundary Layer (PBL) model has been constructed in order to identify important processes that control such changes.The coupled model uses the well-known "big-leaf' model for the vegetation part. Surface resistance (r s ) is described by means of an up-scaled ''A-g s '' model, where stomatal conductance is related to photosynthetic rate. The background of this model for (r s ) is outlined. A new parameterization to mimic stomatal humidity responses is proposed. The parameterization prescribes a linear relation between the specific humidity deficit at the leaf surface and the ratio of the internal C0 2 concentration to the external C0 2 concentration. The resulting ''A-g s '' model simulates stomatal responses to CO 2 , light, temperature, humidity as well as their synergistic interactions. The model is tested using data for grapevines ( VitisVinifera L., cv. Airen). The model is able to simulate the photosynthetic rate and the stomatal conductance of this species satisfactorily.The PBL part of the coupled model is a 1D, first-order closure model, which takes into account nonlocal turbulent transport by means of a countergradient correction. The PBL model also simulates C0 2 fluxes and concentrations. The surface flux of C0 2 is driven by photosynthetic rate from the up-scaled ''A-g s '' model. The complete coupled model realistically simulates the state of the PBL, (r s ) transpiration, and the most important aspects of the biosphere-atmosphere interaction for extensive, homogeneous, well-watered canopies with dry leaves.Systematic sensitivity studies using the coupled model reveal that the interaction between vegetation and the PBL has a significant effect on transpiration and on (r s ) On the one hand, the PBL provides a strong negative feedback on transpiration which reduces the change in the transpiration at given change in (r s ) The influence of the PBL depends strongly on surface roughness. On the other hand, the simultaneous change of (r s ) and of the specific humidity deficit inside the canopy provides a positive feedback, thereby increasing the initial perturbation of (r s ) and transpiration. A second positive feedback mechanism is present if the optimum temperature for photosynthesis is exceeded.The main conclusion is that the interaction between the PBL and vegetation has to be taken into account if transpiration and its changes due to changing surface characteristics are to be predicted at the regional scale

Gemeten actuele verdamping voor twaalf locaties in Nederland

Stowa heeft Alterra de opdracht gegeven jaarreeksen van actuele dagelijkse verdamping af te leiden voor twaalf meetlocaties in Nederland. Daarbij is gebruik gemaakt van bestaande (micro)meteorologische meetgegevens. De meetgegevens zijn gecontroleerd op kwaliteit en continuïteit en ontbrekende dagtotalen zijn aangevuld met door een Artificieel Neuraal Netwerk gesimuleerde gegevens. De onzekerheid in de jaartotalen van de bepaalde actuele verdamping ligt tussen de 10 en 15%

Use of a mobile platform for assessing urban heat stress in Rotterdam

In this study, an assessment of the intensity of the urban heat island (UHI) in Rotterdam was carried out using an innovative mobile bio-meteorological measuring platform mounted on a cargo bicycle. The goal was to assess whether or not heat stress is currently or likely to become a critical issue. Physiological equivalent temperatures were calculated directly from the measurements. Preliminary results show how effective urban parks and greenery are in reducing the UHI. The maximum UHI was about 7 K warmer than the rural area, whereas greener urban configurations were under 3 K warmer. City parks show marked cooling effects during daytime. The preliminary results clearly demonstrate the presence of a considerable UHI in Rotterdam, which is expected to be found in other Dutch cities, and confirms the important role of green spaces in mitigating urban heat stress

Emissions of N2O from fertilized and grazed grassland on organic soil in relation to groundwater level

Intensively managed grasslands on organic soils are a major source of nitrous oxide (N2O) emissions. The Intergovernmental Panel on Climate Change (IPCC) therefore has set the default emission factor at 8 kg N–N2O ha-1 year-1 for cultivation and management of organic soils. Also, the Dutch national reporting methodology for greenhouse gases uses a relatively high calculated emission factor of 4.7 kg N–N2O ha-1 year-1. In addition to cultivation, the IPCC methodology and the Dutch national methodology account for N2O emissions from N inputs through fertilizer applications and animal urine and faeces deposition to estimate annual N2O emissions from cultivated and managed organic soils. However, neither approach accounts for other soil parameters that might control N2O emissions such as groundwater level. In this paper we report on the relations between N2O emissions, N inputs and groundwater level dynamics for a fertilized and grazed grassland on drained peat soil. We measured N2O emissions from fields with different target groundwater levels of 40 cm (‘wet’) and 55 cm (‘dry’) below soil surface in the years 1992, 1993, 2002, 2006 and 2007. Average emissions equalled 29.5 kg N2O–N ha-1 year-1 and 11.6 kg N–N2O ha-1 year-1 for the dry and wet conditions, respectively. Especially under dry conditions, measured N2O emissions exceeded current official estimates using the IPCC methodology and the Dutch national reporting methodology. The N2O–N emissions equalled 8.2 and 3.2% of the total N inputs through fertilizers, manure and cattle droppings for the dry and wet field, respectively and were strongly related to average groundwater level (R 2 = 0.74). We argue that this relation should be explored for other sites and could be used to derive accurate emission data for fertilized and grazed grasslands on organic soil

Modelling and observing urban climate in the Netherlands

Volgens de klimaatscenario’s van het KNMI uit 2006 zal de gemiddelde temperatuur in Nederland in de komende decennia verder stijgen. Hittegolven zullen naar verwachting vaker voorkomen en de intensiteit van met name zomerse buien kan toenemen. In steden zijn de gevolgen van de opwarming extra voelbaar, omdat de temperaturen er door het zogenoemde Urban Heat Island (UHI) effect veel hoger kunnen zijn dan in het omliggende gebied. Zulke periodes met hoge temperaturen gaan veelal gepaard met verslechterde luchtkwaliteit en droogte. Dit alles kan grote gevolgen hebben voor de leefbaarheid en de gezondheid van de bevolking in stedelijke gebieden. Veranderingen in de buienintensiteit beïnvloeden de waterhuishouding van de stad