TEMPERATURE AND PRECIPITATION REGIME IMPACT ON SPRING BARLEY (HORDEUM VULGARE) GROWTH IN PRIEKUĻI CASE

In Latvia, the effects of drought and extreme temperatures on spring barley have so far been little studied due to the availability of data and the fact that meteorological conditions are only one of the multi-influencing factors that affect the agricultural sector.Barley usually flowers before or at the same time as ear emergence. During the flowering period high ambient temperatures are critical for yield formation. If the air temperature during flowering is above 22℃ the flowers of spring barley become sterile. From 2004 - 2022, a significant and positive correlation (R = 0,57) was observed between the average maximum daily temperature from sowing to ear emergence and the number of empty flowers in the main spike. A significant negative correlation (R = 0,55) was observed between plant height and the sum of precipitation from sowing to ear emergence and spike length and the sum of precipitation from ear emergence to maturity (R = −0,54), drought also negatively affects tillering rate and number of productive stems per plant.The combination of all the above-mentioned conditions significantly impacts the yield of barley. The following and relevant findings are very important for the agricultural sector, especially in the context of climate change.

Assessing automated gap imputation of regional scale groundwater level data sets with typical gap patterns

Large groundwater level (GWL) data sets are often patchy with hydrographs containing continuous gaps and irregular measurement frequencies. However, most statistical time series analyses require regular observations, thus hydrographs with larger gaps are routinely excluded from further analysis despite the loss of coverage and representativity of an initially large data set. Missing values can be filled in with different imputation methods, yet the challenge is to assess the imputation performance of automated methods. Assessment of such methods tends to be carried out on randomly introduced missing values. However, large GWL data sets are commonly dominated by more complex patterns of missing values with longer contiguous gaps. This study presents a new artificial gap introduction approach (TGP- typical gap patterns) that improves our understanding of automated imputation performance by mimicking typical gap patterns found in regional scale groundwater hydrographs. Imputation performance of machine learning algorithm missForest and imputePCA is then compared with commonly applied linear interpolation to prepare a gapless daily GWL data set for the Baltic states (Estonia, Latvia, Lithuania). We observed that imputation performance varies among different gap patterns, and performance for all imputation algorithms declined when infilling previously unseen extremes and hydrographs influenced by groundwater abstraction. Further, missForest algorithm substantially outperformed other methods when infilling contiguous gaps (up to 2.5 years), while linear interpolation performs similarly for short random gaps. The TGP approach can be of use to assess the complexity of missing observation patterns in a data set and its value lies in assessing the performance of gap filling methods in a more realistic way. Thus the approach aids the appropriate selection of imputation methods, a task not limited to groundwater level time series alone. The study further provides insights into region-specific data peculiarities that can assist groundwater analysis and modelling

Recent Advances in Tracer‐Aided Mixing Modeling of Water in the Critical Zone

Plain Language Summary: The Critical Zone is a dynamic interface where air, water, soil, plants, and rocks interact. Ensuring sustainable water resources and healthy ecosystems requires understanding how water moves within the Critical Zone and how this may change in the future. To model water partitioning within the Critical Zone, researchers often use tracer‐aided mixing models that allow us to track the movement of water using naturally occurring markers or “tracers.” This approach quantifies the sources and flowpaths of water in the water cycle, from raindrops to aquifers deep below the ground. In this Review, we summarize the latest advancements in tracer‐aided mixing models and how they help us to gain a clearer and more precise understanding of water pathways in the Critical Zone. In addition, we propose future research directions in this evolving field

Twenty-three unsolved problems in hydrology (UPH) – a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come.publishedVersio

Memory effect of soil water regime in wet forests, Norther Europe, Latvia

&amp;lt;p&amp;gt;Forests in hydric (wet) growing conditions are characterised by waterlogged soil conditions for a significant portion of the year with peat layer less than 30 cm. In these locations growth of most tree species is hampered due to lack of oxygen in waterlogged soil, but peat accumulation does not take place as the organic detritus is decomposed during the dry periods. These are marginal ecosystems in between wetlands and drylands and as such are sensitive to climate change. But due to their limited practical value have often been neglected by researchers.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We study the soil water regime of hydric forests constructing Hydrus-1D soil water model. The model was validated with field observations of soil water content, potential and groundwater level at three field sites in Latvia, northern Europe. The meteorological parameters for the model forcing were obtained from the E-obs data set (version v24.0e), including wind speed, relative humidity, incoming shortwave radiation, air temperature and precipitation. Model run period was from 1980 to middle of June 2021.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The model was used to explore the sensitivity of the forest water balance to the crucial parameters such as soil grain size distribution, seasonality and value of the leaf area index (LAI) and canopy surface albedo, and root system ability to compensate lack of water or waterlogged conditions in some part of the soil profile. Preliminary results indicated that there is feedback between soil aeration and transpiration. This can result in a memory effect where increased transpiration leads to soil pore water depletion, better soil aeration and further increase in transpiration and vice versa.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;This work was supported by ERDF postdoctoral research project &amp;amp;#8220;Groundwater and soil water regime&amp;amp;#8221;, under climate change (No. 1.1.1.2/VIAA/3/19/524).&amp;lt;/p&amp;gt;</jats:p

Simulation of vegetation-soil water feedback in nemoral forests on hydromorphic soils with Hydrus-1D

&amp;lt;p&amp;gt;It is hypothesized that northern nemoral forests on hydromorphic soils in lowland settings can enter a feedback loop were enhanced evapotranspiration led to better soil aeration enhancing root water uptake and further increase of evapotranspiration. Opposite feedback could be possible as well &amp;amp;#8211; poor soil aeration due to water saturation hinders the root water uptake, resulting in overall decreased evapotranspiration and preservation of waterlogged state of the soil. The feasibility of the feedback loop is explored by a Hydrus-1D simulation using artificial climate forcing. It is suggested that wet or dry years can shift the vegetation-soil water&amp;lt;strong&amp;gt; &amp;lt;/strong&amp;gt;system from wet to dry state and back. The research is supported by project No. 1.1.1.2/VIAA/3/19/524.&amp;lt;/p&amp;gt;</jats:p

Hands-on activities in climate education at school: three successful examples

&amp;lt;p&amp;gt;According to studies and surveys, Latvian society is sceptical of climate changes &amp;amp;#8211; it is characterised by short-term thinking. STEM teachers acknowledge that the climate issue is one of the most difficult and incomprehensible topics for students. Students' understanding of climate change issues is low because there is poor understanding of concept of the climate itself and physical processes shaping the climate system. Students do not see the consequences and responsibilities of their actions. In addition, there is little climate-related teaching materials available in Latvian language hampering incorporation climate issues in the regular school programs or informal educational activities.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In collaboration with youth NGO, Latvian 4H club, Faculty of Geography and Earth Sciences at University of Latvia have developed several teaching materials, easy-to-read instructions and video demonstration in Latvian for hands on climate education activities. Low-cost and easily available materials and reagents have used for all the activities. Some of the examples: what is the difference in air temperature in a jar with and without CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; heated by incandescent light bulb or how the water pH changes when CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; is bubbled (blown) through it with a straw?&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In the &amp;amp;#8220;60 elements in your pocket&amp;amp;#8221; project, we have dismantled mobile phones and discussed what raw materials have used to build and what are the environmental consequences of extracting them and demonstrating actual mineral samples. We discuss with students what are our consumption habits, and how can everyone mitigate the effects of climate change?&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We strongly believe that hands-on activities have to be a crucial part in any climate-related education program. Experiments and demonstrations need to be simple, understandable, and show the complexity of climate and economic system.&amp;lt;/p&amp;gt; </jats:p

SOIL WATERLOGGING STRESS COMPENSATED BY ROOT SYSTEM ADAPTATION IN A POT EXPERIMENT WITH SWEET CORN ZEA MAYS VAR. SACCHARATE

Soil waterlogging due to excess moisture resulting in hypoxic soil conditions can have detrimental effect on development of many dryland plants growing in locations with temporary water logged soils. Oxygen stress in hypoxic soils can lead to decrease root water uptake and transpiration compared to well aerated soil conditions. In turn reduction of transpiration have a positive effect on soil water budget facilitating the preservation of waterlogged state of the soil. We investigate this phenomenon in a greenhouse pot experiment using sweet corn Zea mays var. saccharate as a model species. After establishment seedlings were subject to a differentiated watering regime ranging for now watering to heavy overwatering resulting in soil waterlogging and flooding. It was observed that the elongation rate of maize seedlings decreased once soil was waterlogged. However soon after soil flooding the elongation reassumed coinciding with appearance of new adventitious roots taping the water layer above flooded soils surface. It is concluded the ability of root system adaptation to change in soil water regime determines the plant species success in sites with periodically waterlogged soils. The feedback between soil aeration status and water uptake can result in swinging between waterlogged and desiccated soil conditions, providing competitive advantages to different sets of species during dry-land and wet-land phases. </jats:p

Comparing tree ring chronology and soil water model for a hydric hemiboreal forest

&amp;lt;p&amp;gt;Air temperature and hence potential evapotranspiration trends are clearly positive worldwide, while precipitation trends are unclear largely due to large inherent variability. Apparently, because of climate change increasing evapotranspiration is likely to lead to depletion of soil water reserves in many ecosystems, but ecosystem feedbacks can have a nonlinear impact of the water regime. For example, in a hemi boreal forest at a hydric setting, higher evapotranspiration due to higher temperatures can lead to improved soil aeration, facilitating the rejuvenation of woody vegetation and further increase of transpiration. Process-based soil water models can be used to investigate such phenomena. However, the models need to be validated. Long time series of the forest soil water regime are sparce. Instead, the tree-ring width data (chronology) can be used as a proxy for growing conditions in the past, as the soil water regime has the firs order controlling factor. We are constructing a Hydrus-1D soil-water model for three hydric forest sample plots in Latvia using the e-obs data set for model forcing. The model results then are compared to the local tree-ring chronology, particularly examining pointer years as extreme cases for evaluating hydrological situation. The model will provide opportunity for scenario investigation of the interactions between climate and soil water regime in hemiboreal forest ecosystem. This work was supported by ERDF postdoctoral research project &amp;amp;#8220;Groundwater and soil water regime under climate change&amp;amp;#8221; (No. 1.1.1.2/VIAA/3/19/524).&amp;lt;/p&amp;gt;</jats:p

Phenological data set of five taxonomic groups and agrarian activities in temperate climate: trends and influencing factors, Latvian case study

&amp;lt;p&amp;gt;A phenological data set collected by volunteers` observers from the Latvia Phenological Observation Network covering period 1970 to 2018 has digitized from original paper based publications in Nature Calendars and analysed. The data set includes more than 40 thousand observations, 148 phenological phases across five different taxonomic groups: insects, amphibian, birds, fungi and plants as well as agrarian activities like sowing, harvesting date and some meteorological parameters like first and late frost, snow, ice regime.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The phenological changes or trends was analysed in two ways: 1. by combining data rows (station-phase-species) for one phase, such as leafing (BBCH11) for all trees and bushes; 2. by performing regression analyses for each phase and for each observation point separately.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;More than 80% of spring data series shows negative tendency as reported in most scientific publications on European phenology. In our data set, overall, autumn phenologies are occurring later over time or the trends are neutral.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Regression analyses of phenology date versus year shows the disparities among species and among locations within a species: spring migrants&amp;amp;#8217; return earlier, while staying longer in the fall with exceptions, for example the white stork in autumn leaves earlier than in the beginning of the period.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The commencement of the agricultural activities in spring such as sowing date have not changed significantly. However, such activities as livestock grazing and sowing of winter cereals takes place latter in the autumn. &amp;amp;#160;These both appear to have affected by both technological changes and changes in meteorological parameters, for example, the trend of first autumn frost and first snow is positive &amp;amp;#8211; they have observed latter.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We have analysed trends and cross correlation with phenology in temperature regime, heat waves, precipitation, drought&amp;amp;#160;indexes, evapotranspiration, and soil temperature for the last 40 years.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Research is supported by the ERDF Project No.&amp;amp;#160;1.1.1.2/VIAA/2/18/265&amp;amp;#160;at the University of Latvia.&amp;lt;/p&amp;gt; </jats:p